add loading of testdata to CI

Author: nuest

.github/workflows/ci.yml

@@ -53,6 +53,10 @@ jobs:
       run: |
         python manage.py migrate
 
+    - name: Load testdata to see if it is up to date with the Django migrations
+      run: |
+        python manage.py loaddata fixtures/test_data.json
+
     - name: Run Tests
       run: |
         python -Wa manage.py test tests