chore(zizmor): pin reusable workflow to @main

Made-with: Cursor

Author: isaiah-grafana

.github/workflows/self-zizmor.yaml

@@ -46,7 +46,7 @@ jobs:
     if: ${{ needs.zizmor-check.outputs.found-files == 'true' }}
 
     # Reusable workflow: zizmor + grafana-bench. Use ref with caller repo name for service/suite (fixes service=security).
-    uses: grafana/shared-workflows/.github/workflows/reusable-zizmor.yml@feat/zizmor-grafana-bench
+    uses: grafana/shared-workflows/.github/workflows/reusable-zizmor.yml@main
     with:
       runs-on: ${{ !github.event.repository.private && 'ubuntu-latest' || 'ubuntu-arm64-small' }}
       fail-severity: high