feat(objectionary#3936): add 'post-comment' workflow

.github/workflows/post-comment.yaml

@@ -0,0 +1,28 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+# yamllint disable rule:line-length
+name: Post Benchmark Comment
+on:
+  workflow_run:
+    workflows: [ "Performance Regression Check" ]
+    types:
+      - completed
+
+jobs:
+  post-comment:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Download Benchmark Comment
+        uses: actions/download-artifact@v4
+        with:
+          name: benchmark-comment
+          run-id: ${{ github.event.workflow_run.id }}
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+      - name: Post Comment on PR
+        uses: mshick/add-pr-comment@v2
+        with:
+          issue: ${{ github.event.workflow_run.pull_requests[0].number }}
+          message-path: |
+            benchmark-comment.md
+          repo-token: ${{ secrets.GITHUB_TOKEN }}