CI: Fix flake8 to exclude dev-tools directory (resolves lint errors)

.github/workflows/main.yml

@@ -79,8 +79,8 @@ jobs:
           black --check .
           # Check import sorting
           isort --check-only .
-          # Run flake8 (fail the job on lint errors) and exclude virtualenv
-          flake8 --max-line-length=88 --exclude venv
+          # Run flake8 (fail the job on lint errors) and exclude virtualenv and dev tools
+          flake8 --max-line-length=88 --exclude venv,dev-tools
       - name: Run tests
         run: |
           pytest