add final tests job to check test matrix (#95)

.github/workflows/test.yml

@@ -63,3 +63,15 @@ jobs:
       - name: Run tests
         run: |
           uv run noxfile.py --session "tests(python='${{ matrix.python-version }}', django='${{ matrix.django-version }}')"
+
+  tests:
+    runs-on: ubuntu-latest
+    needs: test
+    if: always()
+    steps:
+      - name: OK
+        if: ${{ !(contains(needs.*.result, 'failure')) }}
+        run: exit 0
+      - name: Fail
+        if: ${{ contains(needs.*.result, 'failure') }}
+        run: exit 1