Retry Google Auth transport failures

[medisean]

Fixes #2869\n\nSummary:\n- Treat Google Auth TransportError as transient when HttpRetryOptions is enabled.\n- Keep permanent RefreshError failures non-retryable.\n- Add retry predicate coverage.\n\nTests:\n- Python syntax compilation passed.\n- Pytest could not start because the google-auth dependency is unavailable.

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[Venkaiahbabuneelam]

Hi @medisean, Thanks for reaching out us!

Please resolve all conflict checks.
Thanks

[github-actions]

This pull request has been marked as stale because it has been inactive for 14 days with no activity. It will be closed in 2 days if no further activity occurs.

[github-actions]

This pull request was closed because it has been inactive for 16 days. Please reopen or submit a new PR if you need further assistance. Thanks!