Make mypy happy by fixing type annotation

Author: Daniel Gallagher

graphql/execution/tests/test_middleware.py

@@ -143,7 +143,7 @@ def resolve(self, next, *args, **kwargs):
 
 
 def test_middleware_chain(capsys):
-    # type: () -> None
+    # type: (Any) -> None
     class CharPrintingMiddleware(object):
         def __init__(self, char):
             # type: (str) -> None