test(spanner): clear context-aware mTLS env var in unit tests

[sakthivelmanii]

Unset CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE in mTLS unit tests to prevent failures in Google and Kokoro CI environments.

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request updates the GAPIC generator templates and Google Cloud Spanner unit tests to properly handle the CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE environment variable by popping it during mTLS endpoint tests. It also sets GOOGLE_API_USE_CLIENT_CERTIFICATE to "false" when testing specific GOOGLE_API_USE_MTLS_ENDPOINT behaviors. The reviewer recommends also explicitly setting CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE to "false" in those same test cases to avoid test failures in environments where it is set to "true".

[gemini-code-assist]

To prevent test failures in environments where CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE is set to "true", we should also explicitly set it to "false" in this mock.patch.dict call, similar to how GOOGLE_API_USE_CLIENT_CERTIFICATE is handled.

    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "never", "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false", "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false"}):

[gemini-code-assist]

To prevent test failures in environments where CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE is set to "true", we should also explicitly set it to "false" in this mock.patch.dict call, similar to how GOOGLE_API_USE_CLIENT_CERTIFICATE is handled.

    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "always", "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false", "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false"}):