Add GHA script for feature freeze

Author: blyxyas

.github/workflows/feature-freeze.yml

@@ -0,0 +1,25 @@
+name: Feature freeze check
+
+on:
+  pull_request:
+    paths:
+      - 'clippy_lints/src/declared_lints.rs'
+
+jobs:
+  auto-comment:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Check PR Changes
+      id: pr-changes
+      run: echo "::set-output name=changes::${{ toJson(github.event.pull_request.changed_files) }}"
+
+    - name: Create Comment
+      if: steps.pr-changes.outputs.changes != '[]'
+      run: |
+        # Use GitHub API to create a comment on the PR
+        PR_NUMBER=${{ github.event.pull_request.number }}
+        COMMENT="**Seems that you are trying to add a new lint!**\nWe are currently in a [feature freeze](https://doc.rust-lang.org/nightly/clippy/development/feature_freeze.html), so we are delaying all lint-adding PRs to August 1st and focusing on bugfixes.\nThanks a lot for your contribution, and sorry for the inconvenience.\nWith ❤ from the Clippy team"
+        GITHUB_TOKEN=${{ secrets.GITHUB_TOKEN }}
+        COMMENT_URL="https://api.github.com/repos/${{ github.repository }}/issues/${PR_NUMBER}/comments"
+        curl -s -H "Authorization: token ${GITHUB_TOKEN}" -X POST $COMMENT_URL -d "{\"body\":\"$COMMENT\"}"