chore(zizmor): use fork branch ref for shared-workflows pilot

Point reusable-zizmor at isaiah-grafana/shared-workflows feat/zizmor-vendor-excludes-326
so org ruleset testing tracks latest fork pushes without bumping SHAs.

Author: isaiah-grafana

.github/workflows/self-zizmor.yaml

@@ -47,7 +47,8 @@ jobs:
 
     # Testing security-appsec#326: reusable with optional .github/zizmor-collection-ignore. Point org rulesets at
     # branch test/zizmor-vendor-excludes-326 to validate; replace with grafana/shared-workflows@<merge SHA> for main.
-    uses: isaiah-grafana/shared-workflows/.github/workflows/reusable-zizmor.yml@242628b1464cb1ecfb92b208f2bb8aaae795ec63
+    # Pin to fork branch (moves with pushes) for pre-merge testing; switch back to @<SHA> for reproducible runs.
+    uses: isaiah-grafana/shared-workflows/.github/workflows/reusable-zizmor.yml@feat/zizmor-vendor-excludes-326
     with:
       runs-on: ${{ !github.event.repository.private && 'ubuntu-latest' || 'ubuntu-arm64-small' }}
       fail-severity: high