ci: make clang-format check informational instead of blocking

Replace the hard CI failure with a warning annotation and a PR comment
containing the formatting diff. Uses peter-evans/find-comment and
create-or-update-comment to post (or update) a single collapsible
comment per PR. Also bumps actions/checkout to v4.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: UdjinM6

.github/workflows/clang-diff-format.yml

@@ -7,18 +7,66 @@ on:
 jobs:
   ClangFormat:
     runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Fetch git
         run: git fetch --no-tags -fu origin develop:develop
       - name: Run Clang-Format-Diff.py
+        id: clang-format
         run: |
           git diff -U0 origin/develop -- $(git ls-files -- $(cat test/util/data/non-backported.txt)) | ./contrib/devtools/clang-format-diff.py -p1 > diff_output.txt
           if [ -s diff_output.txt ]; then
-              echo "Clang format differences found:"
-              cat diff_output.txt
-              exit 1
+              echo "::warning::Clang format differences found. See PR comment for details."
+              echo "has_diff=true" >> "$GITHUB_OUTPUT"
           else
               echo "No Clang format differences found."
+              echo "has_diff=false" >> "$GITHUB_OUTPUT"
           fi
+      - name: Build comment body
+        if: steps.clang-format.outputs.has_diff == 'true'
+        run: |
+          {
+            echo "<!-- clang-format-check -->"
+            echo "⚠️ Clang Format Diff Check"
+            echo "---"
+            echo ""
+            echo "Formatting issues were found in this PR."
+            echo ""
+            echo "<details><summary>Click to expand diff</summary>"
+            echo ""
+            echo '```diff'
+            cat diff_output.txt
+            echo '```'
+            echo ""
+            echo "</details>"
+          } > comment_body.txt
+      - name: Find existing comment
+        uses: peter-evans/find-comment@v3
+        id: fc
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          comment-author: 'github-actions[bot]'
+          body-includes: '<!-- clang-format-check -->'
+      - name: Post or update comment
+        if: steps.clang-format.outputs.has_diff == 'true'
+        uses: peter-evans/create-or-update-comment@v5
+        with:
+          comment-id: ${{ steps.fc.outputs.comment-id }}
+          issue-number: ${{ github.event.pull_request.number }}
+          edit-mode: replace
+          body-path: comment_body.txt
+      - name: Update comment as resolved
+        if: steps.clang-format.outputs.has_diff == 'false' && steps.fc.outputs.comment-id != ''
+        uses: peter-evans/create-or-update-comment@v5
+        with:
+          comment-id: ${{ steps.fc.outputs.comment-id }}
+          edit-mode: replace
+          body: |
+            <!-- clang-format-check -->
+            ✅ Clang Format Diff Check
+            ---
+
+            No formatting issues found.