ci: install ORAS before publishing OPA bundle

Author: GDYendell

.github/workflows/_policy_container.yaml

@@ -36,6 +36,10 @@ jobs:
           --revision ${{ github.ref_name }}
           --ignore *_test.rego
 
+      - name: Setup ORAS
+        if: ${{ github.event_name == 'push' && startsWith(github.ref, 'refs/tags') }}
+        uses: oras-project/setup-oras@v1
+
       - name: Publish OPA Bundle
         if: ${{ github.event_name == 'push' && startsWith(github.ref, 'refs/tags') }}
         run: >