Acceptance tests fail for PR opened from forked repository

[barbeau]

Describe the bug
The acceptance tests implemented in #848 are important because they detect changes to validation output on all datasets in the MobilityDatabase based on changes to validation rule logic.

However, as seen in #1090 (review), these tests fail to execute for forks of the gtfs-validator repo (i.e., all external contributions to the project):

For information Rule acceptance tests fails because the PR merges code from another github repository that does not have access to the credentials required to set up and authorize the usage GCP.

How we reproduce the bug
Steps to reproduce the behaviour:

1. Fork the gtfs-validator
2. Change code and open a PR

Expected behaviour
Acceptance tests should complete with a report on changes in validation output for MobilityData datasets as seen in #1083 (comment).

Observed behaviour
It appears the reports can't be persisted to Google Cloud storage because of permissions issues on the credentials, causing the process to fail.

Screenshots:
See #1090 (review)

Environment versions

• validator version: Master branch as of d797a13
• Java version: GitHub Action (see master branch)
• OS versions: GitHub Action (see master branch)

[github-actions]

Thank you for your reporting a bug. The issue has been placed in triage, the MobilityData team will follow-up on it.