tests: Handle deprecation warnings in unit tests

[ohmayr]

1. Deprecated credentials_file in google-auth:

The `credentials_file` argument was deprecated by the Google Cloud Auth library (`google-auth`), which is the upstream dependency responsible for handling authentication. The core reason for this deprecation is security.

The new best practice, which the `google-auth` library now promotes, is to use explicit, type-specific loaders.

The google-api-core library (where we are working) uses google-auth for its authentication, so it is passing this deprecation warning along to its users to encourage them to adopt the safer pattern.

This change updates the affected unit tests to explicitly handle these warnings using `pytest.warns()`. The warnings are an expected and correct behavior for deprecated functionality and for Python version support checks.

2. Future warnings are raised for Python 3.10:

FutureWarning: You are using a Python version (3.10.13) which Google will stop supporting in new releases of google.api_core once it reaches its end of life (2026-1...

We're suppressing these warnings in our unit tests but these will be correctly emitted to the user.

3. .nox/unit_w_prerelease_deps-3-14 failing:

The test `test_wrap_method_with_overriding_timeout_as_a_number()` was failing due to an AssertionError.

The purpose of this test is to verify that when a user provides a timeout number (e.g., 22), that number is correctly passed down to the underlying grpc call. It's a "plumbing" test, not a performance or precision timing test. We've adjusted the tolerance to fix this issue.

[parthea]

Add a comment to clarify that credentials_file is deprecated. Applies throughout

[parthea]

We do want to see warnings as that may require code changes. We can filter warnings here with a comment that links to a bug with more information

python-api-core/pyproject.toml

Line 91 in 628003e

filterwarnings = [