test: save pytest warning reports to GHA artifacts

- add pytest_hooks import back in common/lib/conftest.py. This import was removed during refactoring work

.github/workflows/unit-tests.yml

@@ -63,3 +63,47 @@ jobs:
       - name: run tests
         run: |
           python -Wd -m pytest -p no:randomly --ds=${{ env.settings_path }} ${{ env.unit_test_paths }}
+
+      - name: rename warnings json file
+        if: success()
+        run: |
+          cd test_root/log
+          mv pytest_warnings.json pytest_warnings_${{ matrix.shard_name }}.json
+
+      - name: save pytest warnings json file
+        if: success()
+        uses: actions/upload-artifact@v2
+        with:
+          name: pytest-warnings-json
+          path: |
+            test_root/log/pytest_warnings*.json
+
+  compile-warnings-report:
+    runs-on: [ self-hosted ]
+    needs: [ run-tests ]
+    steps:
+      - name: sync directory owner
+        run: sudo chown runner:runner -R .*
+      - uses: actions/checkout@v2
+      - name: collect pytest warnings files
+        uses: actions/download-artifact@v2
+        with:
+          name: pytest-warnings-json
+          path: test_root/log
+
+      - name: display structure of downloaded files
+        run: ls -la test_root/log
+
+      - name: compile warnings report
+        run: |
+          python openedx/core/process_warnings.py --dir-path test_root/log --html-path reports/pytest_warnings/warning_report_all.html
+
+      - name: save warning report
+        if: success()
+        uses: actions/upload-artifact@v2
+        with:
+          name: pytest-warning-report-html
+          path: |
+            reports/pytest_warnings/warning_report_all.html
+
+