fix(publish-to-bcr): disable attestations

FYI @loosebazooka

.github/workflows/publish_to_bcr.yaml

diff --git a/.github/workflows/publish_to_bcr.yaml b/.github/workflows/publish_to_bcr.yaml
index 84fdbb8..aa4dce5 100644
--- a/.github/workflows/publish_to_bcr.yaml
+++ b/.github/workflows/publish_to_bcr.yaml
@@ -24,6 +24,7 @@
   publish:
     uses: bazel-contrib/publish-to-bcr/.github/workflows/publish.yaml@v1.0.0
     with:
+      attest: false # protobuf releases are not created with provenance attestations
       tag_name: ${{ inputs.tag_name }}
       # GitHub repository which is a fork of the upstream where the Pull Request will be opened.
       registry_fork: protocolbuffers/bazel-central-registry