Add pytest coverage comment to PRs

Add MishaKav/pytest-coverage-comment action to post code coverage
summary as a PR comment. Changes include:
- Add pull-requests: write permission
- Add --junitxml=pytest.xml flag for test summary
- Add coverage comment step with per-file breakdown

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Rafi-Microsoft

.github/workflows/test.yml

@@ -28,6 +28,7 @@ on:
 permissions:
   contents: read
   actions: read
+  pull-requests: write
 
 concurrency:
   group: test-${{ github.ref }}
@@ -69,7 +70,19 @@ jobs:
       - name: Run Backend Tests with Coverage
         if: env.skip_backend_tests == 'false'
         run: |
-          pytest --cov=. --cov-report=term-missing --cov-report=xml ./src/tests
+          pytest --cov=. --cov-report=term-missing --cov-report=xml --junitxml=pytest.xml ./src/tests
+
+      - name: Pytest Coverage Comment
+        if: |
+          always() &&
+          github.event_name == 'pull_request' &&
+          github.event.pull_request.head.repo.fork == false &&
+          env.skip_backend_tests == 'false'
+        uses: MishaKav/pytest-coverage-comment@26f986d2599c288bb62f623d29c2da98609e9cd4  # v1.6.0
+        with:
+          pytest-xml-coverage-path: coverage.xml
+          junitxml-path: pytest.xml
+          report-only-changed-files: true
 
       - name: Skip Backend Tests
         if: env.skip_backend_tests == 'true'