Fix python dependency detection

.forgejo/workflows/testing.yml

@@ -13,13 +13,10 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: '3.11'
-          cache: 'pip'
-      - name: Install needed python modules
-        working-directory: core
-        run: cd core && pip3 install -r requirements.prod.txt
+          cache-dependency-path: '**/requirements.prod.txt'
       - name: Run django tests
         working-directory: core
-        run: python3 -m manage.py test
+        run: python3 manage.py test
 
   deploy:
     needs: [test]