GCP credential auth-refresh check gains timeout handling

The GCP credentials validity check used before running the auth refresh command now distinguishes a timeout from an actual valid/invalid result. If the check times out, the refresh command is skipped and a log message notes it's deferring until the API actually rejects the credentials, instead of always re-running the refresh command on any failure or exception as before. If the API had already rejected the credentials before the timeout, the refresh still runs.