test(bigframes): Add BIGFRAMES_TEST_PROJECT override var for nox config

[TrevorBergeron]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request introduces the ability to override the Google Cloud Project ID used in Nox sessions by setting the BIGFRAMES_TEST_PROJECT environment variable. It updates various test, notebook, and benchmark sessions to propagate this override via the GOOGLE_CLOUD_PROJECT environment variable. I have no feedback to provide.

[tswast]

Thanks!