build: fix docs build

[parthea]

In PR #12634, .kokoro/docker/docs/Dockerfile was updated to use ubuntu:24.04. The previous version ubuntu:22.04 had Python 3.10 installed by default. In ubuntu:24.04, Python 3.12 is the default version. We need to restore Python 3.10 which is used in both the docs and docfx nox sessions.

google-cloud-python/packages/google-cloud-access-approval/noxfile.py

Line 36 in 81f6e2b

DEFAULT_PYTHON_VERSION = "3.10"

google-cloud-python/packages/google-cloud-access-approval/noxfile.py

Lines 290 to 291 in 81f6e2b

	@nox.session(python=DEFAULT_PYTHON_VERSION)
	def docs(session):

google-cloud-python/packages/google-cloud-access-approval/noxfile.py

Lines 325 to 326 in 81f6e2b

	@nox.session(python=DEFAULT_PYTHON_VERSION)
	def docfx(session):

I tested that this builds successfully by running docker build -t test_docs_mono_repo . in the directory kokoro/docker/docs

I then ran the nox sessions docs and docfx.

Use this command to run the docker container and enter into bash

docker run --rm -it --entrypoint /bin/bash test_docs_mono_repo

Then in the docker container, run the following commands

git clone https://github.com/googleapis/google-cloud-python.git
cd google-cloud-python/packages/google-cloud-access-approval
nox -s docs
nox -s docfx