diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index e5d7e064f55e..c5e532ec7217 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -22,18 +22,18 @@ jobs:
       matrix:
         include:
           - name-suffix: "(Minimum Versions)"
-            os: ubuntu-16.04
+            os: ubuntu-18.04
             python-version: 3.7
             extra-requirements: '-c requirements/testing/minver.txt'
             pyqt5-ver: '==5.8 sip==4.19.7'  # oldest versions with a Py3.7 wheel.
             delete-font-cache: true
             XVFB_RUN: xvfb-run -a
-          - os: ubuntu-16.04
+          - os: ubuntu-18.04
             python-version: 3.7
             extra-requirements: '-r requirements/testing/extra.txt'
             XVFB_RUN: xvfb-run -a
             CFLAGS: "-fno-lto"  # Ensure that disabling LTO works.
-          - os: ubuntu-16.04
+          - os: ubuntu-18.04
             python-version: 3.8
             extra-requirements: '-r requirements/testing/extra.txt'
             XVFB_RUN: xvfb-run -a
@@ -128,10 +128,10 @@ jobs:
             ~/.cache/matplotlib
             !~/.cache/matplotlib/tex.cache
             !~/.cache/matplotlib/test_cache
-          key: ${{ runner.os }}-py${{ matrix.python-version }}-mpl-${{ github.ref }}-${{ github.sha }}
+          key: 1-${{ runner.os }}-py${{ matrix.python-version }}-mpl-${{ github.ref }}-${{ github.sha }}
           restore-keys: |
-            ${{ runner.os }}-py${{ matrix.python-version }}-mpl-${{ github.ref }}-
-            ${{ runner.os }}-py${{ matrix.python-version }}-mpl-
+            1-${{ runner.os }}-py${{ matrix.python-version }}-mpl-${{ github.ref }}-
+            1-${{ runner.os }}-py${{ matrix.python-version }}-mpl-
 
       - name: Install Python dependencies
         run: |
@@ -156,12 +156,8 @@ jobs:
           # libraries cannot be loaded at runtime, so an actual import is a
           # better check).
           if [[ "${{ runner.os }}" != 'macOS' ]]; then
-            # PyGObject, pycairo, and cariocffi do not install on OSX 10.12;
-            # pycairo 1.20+ requires a new version of Cairo, unavailable on
-            # Ubuntu 16.04, so PyGObject must be installed without build
-            # isolation in order to pick up the lower pre-installed version.
-             python -m pip install --upgrade 'pycairo<1.20.0' 'cairocffi>=0.8' &&
-             python -m pip install --upgrade --no-build-isolation PyGObject &&
+            # PyGObject, pycairo, and cariocffi do not install on OSX 10.12.
+             python -m pip install --upgrade pycairo 'cairocffi>=0.8' PyGObject &&
                python -c 'import gi; gi.require_version("Gtk", "3.0"); from gi.repository import Gtk' &&
                echo 'PyGObject is available' ||
                echo 'PyGObject is not available'
@@ -180,7 +176,7 @@ jobs:
                echo 'PySide2 is not available'
           fi
           python -m pip install --upgrade \
-            -f https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-16.04 \
+            -f https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-18.04 \
             wxPython &&
             python -c 'import wx' &&
             echo 'wxPython is available' ||
@@ -226,3 +222,9 @@ jobs:
         if: ${{ runner.os != 'macOS' }}
       - name: Upload code coverage
         uses: codecov/codecov-action@v1
+
+      - uses: actions/upload-artifact@v2
+        if: failure()
+        with:
+          name: "${{ matrix.python-version }} ${{ matrix.os }} ${{ matrix.name-suffix }} result images"
+          path: ./result_images
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 2ff87d0c71da..2c25a7786288 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -6,13 +6,13 @@
 strategy:
   matrix:
     Linux_py37:
-      vmImage: 'ubuntu-16.04'
+      vmImage: 'ubuntu-18.04'
       python.version: '3.7'
     Linux_py38:
-      vmImage: 'ubuntu-16.04'
+      vmImage: 'ubuntu-18.04'
       python.version: '3.8'
     Linux_py39:
-      vmImage: 'ubuntu-16.04'
+      vmImage: 'ubuntu-18.04'
       python.version: '3.9'
     macOS_py37:
       vmImage: 'macOS-10.15'
diff --git a/lib/matplotlib/backends/backend_pgf.py b/lib/matplotlib/backends/backend_pgf.py
index 9d01f603e021..522418544bd1 100644
--- a/lib/matplotlib/backends/backend_pgf.py
+++ b/lib/matplotlib/backends/backend_pgf.py
@@ -968,6 +968,9 @@ def __init__(self, filename, *, keep_empty=True, metadata=None):
             'Creator', 'Producer', 'CreationDate', 'ModDate', and
             'Trapped'. Values have been predefined for 'Creator', 'Producer'
             and 'CreationDate'. They can be removed by setting them to `None`.
+
+            Note that some versions of LaTeX engines may ignore the 'Producer'
+            key and set it to themselves.
         """
         self._output_name = filename
         self._n_figures = 0
diff --git a/lib/matplotlib/tests/baseline_images/test_backend_pgf/pgf_mixedmode.pdf b/lib/matplotlib/tests/baseline_images/test_backend_pgf/pgf_mixedmode.pdf
index fdbb20349c42..fd7cf7a5c0d1 100644
Binary files a/lib/matplotlib/tests/baseline_images/test_backend_pgf/pgf_mixedmode.pdf and b/lib/matplotlib/tests/baseline_images/test_backend_pgf/pgf_mixedmode.pdf differ
diff --git a/lib/matplotlib/tests/test_backend_pgf.py b/lib/matplotlib/tests/test_backend_pgf.py
index 75f50ecbf0d9..040b2e714655 100644
--- a/lib/matplotlib/tests/test_backend_pgf.py
+++ b/lib/matplotlib/tests/test_backend_pgf.py
@@ -257,13 +257,17 @@ def test_pdf_pages_metadata_check(monkeypatch, system):
     if '/PTEX.Fullbanner' in info:
         del info['/PTEX.Fullbanner']
 
+    # Some LaTeX engines ignore this setting, and state themselves as producer.
+    producer = info.pop('/Producer')
+    assert producer == f'Matplotlib pgf backend v{mpl.__version__}' or (
+            system == 'lualatex' and 'LuaTeX' in producer)
+
     assert info == {
         '/Author': 'me',
         '/CreationDate': 'D:19700101000000Z',
         '/Creator': f'Matplotlib v{mpl.__version__}, https://matplotlib.org',
         '/Keywords': 'test,pdf,multipage',
         '/ModDate': 'D:19680801000000Z',
-        '/Producer': f'Matplotlib pgf backend v{mpl.__version__}',
         '/Subject': 'Test page',
         '/Title': 'Multipage PDF with pgf',
         '/Trapped': '/True',