[gunicorn] Fix validate_post_request annotation

Author: eugeneliukindev

stubs/gunicorn/gunicorn/config.pyi

@@ -184,7 +184,7 @@ def validate_class(val: object) -> object: ...
 def validate_callable(arity: int) -> Callable[[str | _HookType], _HookType]: ...
 def validate_user(val: int | str | None) -> int: ...
 def validate_group(val: int | str | None) -> int: ...
-def validate_post_request(val: str | _ValidatorType) -> _PostRequestHookType: ...
+def validate_post_request(val: str | _HookType) -> _PostRequestHookType: ...
 def validate_chdir(val: str) -> str: ...
 @overload
 def validate_statsd_address(val: str) -> _AddressType: ...