enable mypy_test for python 3.10 (#5341)

* enable mypy_test for python 3.10

* avoid collections.Mapping and collections.MutableMapping, import from typing

stubs/requests/requests/packages/urllib3/_collections.pyi

@@ -1,5 +1,4 @@
-from collections import MutableMapping
-from typing import Any, NoReturn, TypeVar
+from typing import Any, MutableMapping, NoReturn, TypeVar
 
 _KT = TypeVar("_KT")
 _VT = TypeVar("_VT")