Update docker-gcp.yml

Author: jimbrig

.github/workflows/docker-gcp.yml

@@ -38,7 +38,7 @@ jobs:
         uses: google-github-actions/auth@v2
         with:
           token_format: 'access_token'
-          credentials_json: ${{ env.GCP_SERVICE_ACCOUNT_CREDENTIALS }}
+          credentials_json: ${{ env.GCP_SA_KEY }}
 
       - name: Set up Cloud SDK
         id: setup-cloud-sdk