chore: Run kotoha-chan on GitHub Actions

Author: ftnext

.github/workflows/on-stage.yaml

@@ -11,5 +11,11 @@ jobs:
           curl -LsSf https://astral.sh/uv/install.sh | sh
           uv --version
           uvx --version
+      - name: Play baseball
+        run: |
+          cat > baseball.py <<PY
+          def plus_one(numbers: list[int]) -> list[int]:
+              return [n + 1 for n in numbers]
+          PY
       - name: Run flake8-kotoha
-        run: uvx --with flake8-kotoha flake8 --help
+        run: uvx --with flake8-kotoha flake8 baseball.py; [ $? -eq 1 ]