chore(python): Add Python 3.12

[m-strzelczyk]

Following what #1742 did.

[parthea]

Thanks for putting this together @m-strzelczyk ! Please could you also help with testing in a downstream repo, for example python-bigquery-storage?

I think we may need to add python 3.12 support in https://github.com/googleapis/testing-infra-docker/blob/c02d27d75de5d8f4edb90568e15f42bd9d400c91/python/googleapis/python-multi/Dockerfile#L122 which is for the gcr.io/cloud-devrel-kokoro-resources/python-multi:latest image used in the Kokoro Prerelease Dependencies . For example, see this check in python-bigquery-storage.

To test the changes, run the following command in a clone of this repo (in the specific branch where you made changes)

docker build -f docker/owlbot/python/Dockerfile -t python312 .

Then in a downstream repo such as https://github.com/googleapis/python-bigquery-storage, run

docker run --user $(id -u):$(id -g) --rm -v $(pwd):/repo -w /repo python312

[m-strzelczyk]

I ran the commands you mentioned, but I'm not sure that it actually tested the new python-multi image. I did build the docker/owlbot/python/Dockerfile image and used it on python-bigquery-storage - it seems to only run black on the source code.

Not sure how to locally replicate the whole build and test process that actually runs inside the python-multi on Kokoro.

I did similar changes to python-docs-samples/.kokoro/docker/Dockerfile in #10930 and it worked fine there. As far as I can see, those Dockerfiles are almost identical.

[parthea]

In the monorepo we use the latest python runtime in the prerelease_deps nox session. I think we need this change in split repositories to help with the roll out of the new runtime. Unrelated to your changes, could you please update the file synthtool/gcp/templates/python_library/noxfile.py.j2 to use the latest python version for the prerelease_deps nox session in split repos?

synthtool/synthtool/gcp/templates/python_mono_repo_library/noxfile.py.j2

Lines 419 to 420 in 74ed3eb

	@nox.session(python="{{ unit_test_python_versions | last }}")
	def prerelease_deps(session):

synthtool/synthtool/gcp/templates/python_library/noxfile.py.j2

Lines 410 to 411 in 74ed3eb

	@nox.session(python=SYSTEM_TEST_PYTHON_VERSIONS)
	def prerelease_deps(session):

[parthea]

Will address #1903 (comment) in a separate PR