ci(gcp): read OIDC audience from GCP_ALLOWED_AUDIENCES secret

Author: james00012

.github/workflows/gcp-integration-tests.yml

@@ -67,10 +67,7 @@ jobs:
         with:
           workload_identity_provider: ${{ secrets.GCP_WORKLOAD_IDENTITY_PROVIDER_ID }}
           service_account: ${{ secrets.GCP_SA_EMAIL }}
-          # Must match the provider's oidc.allowedAudiences. The pool was created
-          # following the Google docs that recommend allowed_audiences=
-          # https://github.com/<org>, so we request that audience explicitly here.
-          audience: https://github.com/gruntwork-io
+          audience: ${{ secrets.GCP_ALLOWED_AUDIENCES }}
 
       - name: Set up gcloud CLI
         uses: google-github-actions/setup-gcloud@v2