Fix opm render failure due to v1-format registries.conf

Recent versions of the containers/image library (used by opm) now
hard-error on v1-format registries.conf instead of silently converting
it. GitHub Actions ubuntu-latest runners ship with a v1-format config
at /etc/containers/registries.conf, breaking the "Create index image"
step for all operators using this reusable workflow.

Set CONTAINERS_REGISTRIES_CONF=/dev/null for the opm steps. This is
safe because opm render pulls by fully-qualified image reference and
does not need local registry aliasing.

See also: operator-framework/operator-lifecycle-manager#3839

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lmiccini

.github/workflows/reusable-build-operator.yaml

@@ -298,6 +298,10 @@ jobs:
         INDEX_IMAGE_TAG: ${{ env.latesttag }}
         INDEX_IMAGE: ${{ inputs.operator_name }}-operator-index
         CSV_VERSION: v${{ steps.get_csv_version.outputs.version }}
+        # opm uses containers/image which now rejects v1-format registries.conf
+        # shipped on ubuntu-latest runners. Safe to bypass since opm render
+        # pulls by fully-qualified reference and needs no registry aliases.
+        CONTAINERS_REGISTRIES_CONF: /dev/null
 
     - name: Push ${{ inputs.operator_name }}-operator-index To ${{ env.imageregistry }}
       uses: redhat-actions/push-to-registry@v2