Add a CI job to check that schema deltas are in the correct folder. (#13063)

.github/workflows/tests.yml

@@ -19,6 +19,14 @@ jobs:
       - run: scripts-dev/generate_sample_config.sh --check
       - run: scripts-dev/config-lint.sh
 
+  check-schema-delta:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+      - run: "pip install 'click==8.1.1' 'GitPython>=3.1.20'"
+      - run: scripts-dev/check_schema_delta.py --force-colors
+
   lint:
     uses: "matrix-org/backend-meta/.github/workflows/python-poetry-ci.yml@v1"
     with:
@@ -48,7 +56,7 @@ jobs:
   # Dummy step to gate other tests on without repeating the whole list
   linting-done:
     if: ${{ !cancelled() }} # Run this even if prior jobs were skipped
-    needs: [lint, lint-crlf, lint-newsfile, check-sampleconfig]
+    needs: [lint, lint-crlf, lint-newsfile, check-sampleconfig, check-schema-delta]
     runs-on: ubuntu-latest
     steps:
       - run: "true"