Fix isort w.r.t. _ast/_collections_abc/_tracemalloc/_warnings (#6329)

stdlib/ast.pyi

@@ -8,11 +8,10 @@
 # sys.
 import sys
 import typing as _typing
+from _ast import *  # type: ignore
 from typing import Any, Iterator, TypeVar, overload
 from typing_extensions import Literal
 
-from _ast import *  # type: ignore
-
 if sys.version_info >= (3, 8):
     class Num(Constant):
         value: complex