fix typing

Author: blueyed

src/_pytest/capture.py

@@ -79,7 +79,7 @@ def __init__(self, method):
         self._method = method
         self._global_capturing = None
         self._current_item = None
-        self._atexit_funcs: List[Callable] = []
+        self._atexit_funcs = []  # type: List[Callable]
         atexit.register(self._atexit_run)
         self._tmpfiles = {}