Fix #4260: autodoc: keyword only argument separator is not disappeared

tests/conftest.py

@@ -21,6 +21,9 @@ pytest_plugins = 'sphinx.testing.fixtures'
 collect_ignore = ['roots']
 
 # Disable Python version-specific
+if sys.version_info < (3,):
+    collect_ignore += ['py3']
+
 if sys.version_info < (3, 5):
     collect_ignore += ['py35']