github: Run ruff

Author: jelmer

.github/workflows/test.yml

@@ -43,6 +43,10 @@ jobs:
         run: |
           python -W once -m testtools.run testrepository.tests.test_suite
 
+      - name: Lint
+        run: |
+          ruff check .
+
       - name: Check formatting
         run: |
           ruff format --check .