Add a type: ignore as a hacky workaround for some mypy bazel issues (#2887)

stdlib/3/ast.pyi

@@ -7,7 +7,11 @@ import sys
 import typing as _typing
 from typing import Any, Iterator, Optional, Union, TypeVar
 
-from _ast import *
+# The same unorthodox Bazel integration causes issues with sys, which
+# is imported in both modules. unfortunately we can't just rename sys,
+# since mypy only supports version checks with a sys that is named
+# sys.
+from _ast import *  # type: ignore
 
 class NodeVisitor():
     def visit(self, node: AST) -> Any: ...