* Add Python 3.13 support

This commit introduces support for Python 3.13 as a runtime dependency.

The following changes were made:
- Updated `noxfile.py` to include Python 3.13 in unit and system test versions.
- Created `testing/constraints-3.13.txt` (initially empty, copied from an empty constraints-3.12.txt).
- Updated `.github/workflows/unittest.yml` to include Python 3.13 in the test matrix.
- Updated `setup.py` to add the Python 3.13 classifier.
- Updated `CONTRIBUTING.rst` to list Python 3.13 as a supported version.
- Created `.kokoro/presubmit/system-3.13.cfg` for Kokoro system tests.
- Updated `.github/sync-repo-settings.yaml` to include Python 3.13 in required status checks.
- Updated `owlbot.py` to include Python 3.13 in unit and system test versions for templated files.

* feat: Add Python 3.13 support

This commit introduces support for Python 3.13 as a runtime dependency.

The following changes were made:
- Updated `noxfile.py` to include Python 3.13 in unit and system test versions.
- Created `testing/constraints-3.13.txt` (initially empty, copied from an empty constraints-3.12.txt).
- Updated `.github/workflows/unittest.yml` to include Python 3.13 in the test matrix.
- Updated `setup.py` to add the Python 3.13 classifier.
- Updated `CONTRIBUTING.rst` to list Python 3.13 as a supported version.
- Created `.kokoro/presubmit/system-3.13.cfg` for Kokoro system tests.
- Updated `.github/sync-repo-settings.yaml` to include Python 3.13 in required status checks.
- Updated `owlbot.py` to include Python 3.13 in unit and system test versions for templated files.

* removes presubmit task for 3.12 now that we have one for 3.13

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* Update CONTRIBUTING.rst

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

* Remove support for Python 3.8

This commit removes Python 3.8 from the supported versions.
Updates include changes in noxfiles, GitHub workflows, setup.py,
Kokoro configurations, and documentation to reflect Python 3.9
as the minimum supported version.

* Apply follow-up changes for Python 3.8 removal

This commit addresses items missed in the initial Python 3.8 removal:

* Adds `kokoro/presubmit/system-3.9.cfg`.
* Updates example commands in `CONTRIBUTING.rst`.
* Modifies the warning in `pandas_gbq/__init__.py` for Python < 3.9.
* Updates Python versions in `owlbot.py`.
* Removes 3.8-specific line from `samples/snippets/requirements.txt`.
* Populates `testing/constraints-3.9.txt` with correct lower bounds.

* Update pandas_gbq/__init__.py

* Update samples/snippets/noxfile.py

* Update requirements.txt

* Update testing/constraints-3.9.txt

* Update owlbot.py

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

* chore(deps): update all dependencies

* updates some configs in owlbot, noxfile, and ymls to ensure that the correct version of python is used

* Update noxfile.py

* Update noxfile.py

* Update noxfile.py

---------

Co-authored-by: Mend Renovate <bot@renovateapp.com>

Release-As: 0.29.2

* chore(main): release 0.29.2

* Update CHANGELOG.md

---------

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>
Co-authored-by: Chalmer Lowe <chalmerlowe@google.com>