Google GitHub actions need to be updated

[matthiasrohmer]

See: https://github.com/ampproject/amp.dev/runs/4678421175?check_suite_focus=true#step:6:19

Authentication is now handled by a separate action. This blocks build.

[sebastianbenz]

Afaik, this isn't blocking the build yet (but the service keys expired).

[sebastianbenz]

(and thanks for investigationg :-) )

[matthiasrohmer]

You're welcome! I can also take care of updating the other things tomorrow now the keys are valid again 🙂