Breaking changes in pyfcm 2.1.0 where explicit project_id is set

Summary

This commit adjusted the way the project_id is used when FCMNotification is instantiated:
https://github.com/olucurious/PyFCM/commit/80fec94ce99a70277a33f7983b1f0fdf796ccdee

We run a cloud function which does push notifications in a different project to the firebase project. The service account exists in a different project.

Details

We instantiate FCMNotification like this:

    push_service = FCMNotification(
        service_account_file=service_account_file,
        project_id="firebase-project",
    )

That project_id will never be used if you have a service account:
https://github.com/olucurious/PyFCM/blob/c94dc6d64e7e33c30b4442a172fb24f2e02f8dd1/pyfcm/baseapi.py#L89

Our service account is in a different project:

{
  "type": "service_account",
  "project_id": "backend-project",
  "private_key_id": "<redacted>",
  "private_key": "<redacted>",
  "client_email": "<redacted>",
  "client_id": "<redacted>",
  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
  "token_uri": "https://oauth2.googleapis.com/token",
  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/sepush-push-topics%40sepush-backend.iam.gserviceaccount.com",
  "universe_domain": "googleapis.com"
}

Recommendation

Adjust this code:
https://github.com/olucurious/PyFCM/blob/c94dc6d64e7e33c30b4442a172fb24f2e02f8dd1/pyfcm/baseapi.py#L89

To be:

project_id = self._project_id or getattr(self.credentials, "project_id", None)

Start in pyfcm/baseapi.py at the referenced line in the project_id handling, then compare it with the linked commit and the FCMNotification instantiation shown in the issue. Done means an explicitly supplied project_id is still used when service-account credentials contain a different project_id.