Adapt tests to updated version of google-oauth-plugin

[aneveux]

Supersedes #263

Hello 👋

Since jenkinsci/google-oauth-plugin#186, the constructor public GoogleRobotPrivateKeyCredentials(String projectId, ServiceAccountConfig serviceAccountConfig, @Nullable GoogleRobotCredentialsModule module) was deprecated in favor of one allowing to specify explicitly the credential ID.
This PR provides an update in the automated tests making use of the up-to-date constructor.

Testing done

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