Update dessant/repo-lockdown action to v4 (#43238)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/14650389914

Upstream-Ref: Automattic/jetpack@51ca432

Author: anomiex

.github/workflows/readonly.yml

@@ -10,7 +10,7 @@ jobs:
   lockdown:
     runs-on: ubuntu-latest
     steps:
-      - uses: dessant/repo-lockdown@v2
+      - uses: dessant/repo-lockdown@v4
         with:
           github-token: ${{ github.token }}
           issue-comment: |