Update dessant/repo-lockdown action to v5 (#46347)

Co-authored-by: Renovate Bot <[email protected]>

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/20317564988

Upstream-Ref: Automattic/jetpack@5af43d7

Author: anomiex

.github/workflows/readonly.yml

@@ -15,7 +15,7 @@ jobs:
   lockdown:
     runs-on: ubuntu-latest
     steps:
-      - uses: dessant/repo-lockdown@v4
+      - uses: dessant/repo-lockdown@v5
         with:
           github-token: ${{ github.token }}
           issue-comment: |