Unit tests fail with `google-auth==2.42.0`

[ohmayr]

google-auth 2.42.0 introduces a change that isn't compatible with google-auth-oauthlib. Specifically googleapis/google-auth-library-python@36ecb1d which results in the unit tests to fail. Remove the upper bound once the issue is resolved.

Reproduce the issue with google-auth==2.42.0 and run nox -s unit-3.11.

[daniel-sanche]

Fixed in #433