Use PEP 604 syntax wherever possible (#7493)

stubs/docopt/docopt.pyi

@@ -1,8 +1,8 @@
-from typing import Any, Iterable, Union
+from typing import Any, Iterable
 
 __version__: str
 
-_Argv = Union[Iterable[str], str]
+_Argv = Iterable[str] | str
 
 def docopt(
     doc: str, argv: _Argv | None = ..., help: bool = ..., version: Any | None = ..., options_first: bool = ...