fix(ci): run linter in CI

We were not actually running the linter in CI (despite the name of the
job saying so)

.github/workflows/testing.yml

@@ -34,7 +34,8 @@ jobs:
       - name: Run linting tools
         run: |
           cd app/
-          ruff format .
+          ruff format --diff .
+          ruff check --diff .
       - name: Create logging folder
         run: |
           sudo  mkdir -p /logging