Use PROJECT_ID from environment (#9)

While it's possible to use `PROJECT_ID` from a secret, as it's already
in the environment we should read from there.

Author: henrybell

workflows/create-cloud-deploy-release/cloud-deploy-to-cloud-run.yml

@@ -108,7 +108,7 @@ jobs:
       - name: 'Set up Cloud SDK'
         uses: 'google-github-actions/setup-gcloud@v1'
         with:
-          project_id: '${{ secrets.PROJECT_ID }}'
+          project_id: '${{ env.PROJECT_ID }}'
 
       - name: 'Docker auth'
         run: |-