[3.8] Pin test runner to Ubuntu 18 to un-break CI (GH-24715) (GH-24717)

miss-islington · web-flow · commit 9c6c5da55f4b · 2021-03-03T01:56:41.000-08:00
(cherry picked from commit 94894dd) Co-authored-by: Brandt Bucher <brandt@python.org> Automerge-Triggered-By: GH:tiran
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
@@ -114,7 +114,7 @@ jobs:
 
   build_ubuntu:
     name: 'Ubuntu'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
     needs: check_source
     if: needs.check_source.outputs.run_tests == 'true'
     env:
