Apply ruff/flake8-pytest-style rule PT004

PT004 Fixture does not return anything, add leading underscore

mriqc/tests/test_main.py

@@ -29,7 +29,7 @@
 
 
 @pytest.fixture(autouse=True)
-def set_command(monkeypatch):
+def _set_command(monkeypatch):
     with monkeypatch.context() as m:
         m.setattr(sys, 'argv', ['mriqc'])
         yield