chore(ci): add warning for external contributors force pushing (#4373)

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## Summary\*

This PR adds a sticky comment to any PRs which are opened from another
repository which warns against force pushing once we've started
reviewing the PR.

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[Exceptional Case]** Documentation to be submitted in a separate
PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

---------

Co-authored-by: jfecher <[email protected]>

.github/EXTERNAL_CONTRIBUTOR_PR_COMMENT.md

@@ -0,0 +1,5 @@
+Thank you for your contribution to the Noir language.
+
+Please **do not force push to this branch** after the Noir team have reviewed this PR. Doing so will only delay us merging your PR as we will need to start the review process from scratch.
+
+Thanks for your understanding.

.github/workflows/pull-request-title.yml

@@ -27,3 +27,18 @@ jobs:
             fix
             feat
             chore
+
+  force-push-comment:
+    name: Warn external contributors about force-pushing
+    runs-on: ubuntu-latest
+    if: github.repository != 'noir-lang/noir' && github.event_name == 'pull_request_target'
+    permissions:
+      pull-requests: write
+
+    steps:
+      - name: Post comment on force pushes
+        uses: marocchino/sticky-pull-request-comment@v2
+        with:
+          path: ./.github/EXTERNAL_CONTRIBUTOR_PR_COMMENT.md
+
+