Don't require USE_ADC_CREDENTIALS=1 to run tests.

[tylere]

Instead use ADC credentials if GOOGLE_APPLICATION_CREDENTIALS does not exist. This allows tests to be run without setting an environment variable, which is required by VSCode's Testing (test discovery and management).

[naschmitz]

This looks okay to me. Could you also update https://github.com/google/Xee?tab=readme-ov-file#how-to-run-integration-tests?

[tylere]

The automated tests are failing with

Error: google-github-actions/auth failed with: retry function failed after 4 attempts: the GitHub Action workflow must specify exactly one of "workload_identity_provider" or "credentials_json"! If you are specifying input values via GitHub secrets, ensure the secret is being injected into the environment. By default, secrets are not passed to workflows triggered from forks, including Dependabot.

I don't have access to the repo secrets. @naschmitz could you look at this?

[naschmitz]

The automated tests are failing with

Error: google-github-actions/auth failed with: retry function failed after 4 attempts: the GitHub Action workflow must specify exactly one of "workload_identity_provider" or "credentials_json"! If you are specifying input values via GitHub secrets, ensure the secret is being injected into the environment. By default, secrets are not passed to workflows triggered from forks, including Dependabot.

I don't have access to the repo secrets. @naschmitz could you look at this?

I think this is because the integration tests are running on a fork. We should be good to submit it.