Fix crash when running mypy master against typeshed master (#7660)

stdlib/builtins.pyi

@@ -22,22 +22,11 @@ from _typeshed import (
     SupportsTrunc,
     SupportsWrite,
 )
-from collections.abc import (
-    Awaitable,
-    Callable,
-    Iterable,
-    Iterator,
-    Mapping,
-    MutableMapping,
-    MutableSet,
-    Reversible,
-    Set as AbstractSet,
-    Sized,
-)
+from collections.abc import Awaitable, Callable, Iterable, Iterator, MutableSet, Reversible, Set as AbstractSet, Sized
 from io import BufferedRandom, BufferedReader, BufferedWriter, FileIO, TextIOWrapper
 from types import CodeType, TracebackType, _Cell
 
-# mypy crashes if any of {ByteString, Sequence, MutableSequence} are imported from collections.abc in builtins.pyi
+# mypy crashes if any of {ByteString, Sequence, MutableSequence, Mapping, MutableMapping} are imported from collections.abc in builtins.pyi
 from typing import (  # noqa: Y027
     IO,
     Any,
@@ -45,6 +34,8 @@ from typing import (  # noqa: Y027
     ByteString,
     ClassVar,
     Generic,
+    Mapping,
+    MutableMapping,
     MutableSequence,
     NoReturn,
     Protocol,