fix: Allow protobuf 6.x

[parthea]

Apply changes from googleapis/gapic-generator-python#2352 and googleapis/gapic-generator-python#2347 to 4 packages containing protobuf stubs which are not automatically generated using gapic-generator-python

fix: resolve issue where pre-release versions of dependencies are installed

[parthea]

presubmit core_deps_from_source failed https://github.com/googleapis/google-cloud-python/actions/runs/13775554603/job/38523909038

~/work/google-cloud-python/google-cloud-python/packages/google-cloud-access-context-manager ~/work/google-cloud-python/google-cloud-python
nox > Error while collecting sessions.
nox > Sessions not found: core_deps_from_source

This was fixed by 346097d

[vchudnov-g]

Suggested change

	Pre-releases versions can be installed using
	Pre-release versions can be installed using

[vchudnov-g]

Do you want a -e here like in the previous test?

[vchudnov-g]

Consistency with the other test:

Suggested change

	unit_deps_all = UNIT_TEST_STANDARD_DEPENDENCIES + UNIT_TEST_EXTERNAL_DEPENDENCIES
	# Install dependencies for the unit test environment
	# Install dependencies for the unit test environment
	unit_deps_all = UNIT_TEST_STANDARD_DEPENDENCIES + UNIT_TEST_EXTERNAL_DEPENDENCIES

[vchudnov-g]

Consistency with the other test:

Suggested change

	system_deps_all = (
	SYSTEM_TEST_STANDARD_DEPENDENCIES
	+ SYSTEM_TEST_EXTERNAL_DEPENDENCIES
	+ SYSTEM_TEST_EXTRAS
	)
	# Install dependencies for the system test environment
	# Install dependencies for the system test environment
	system_deps_all = (
	SYSTEM_TEST_STANDARD_DEPENDENCIES
	+ SYSTEM_TEST_EXTERNAL_DEPENDENCIES
	+ SYSTEM_TEST_EXTRAS
	)

[vchudnov-g]

Consistency with previous

Suggested change

	# constraints file containing all dependencies and extras that should be installed.
	# constraints file containing all dependencies and extras.

[vchudnov-g]

Maybe make it clear it's the local source, as opposed to checking it out from somewhere?

Suggested change

	def core_deps_from_source(session, protobuf_implementation):
	def core_deps_from_local_source(session, protobuf_implementation):

[vchudnov-g]

This list is shorter than the corresponding prerel_deps in the previous test. Can we make that one shorter as well? Or does this list include transitive dependencies that are not included in the other? We should explain why they don't correspond.