Add support for PEP 585 generics

Author: Gobot1234

sphinx/util/typing.py

@@ -310,6 +310,8 @@ def stringify(annotation: Any) -> str:
         return INVALID_BUILTIN_CLASSES[annotation]
     elif (getattr(annotation, '__module__', None) == 'builtins' and
           hasattr(annotation, '__qualname__')):
+        if hasattr(annotation, '__args__'):  # PEP 585 generic
+            return repr(annotation)
         return annotation.__qualname__
     elif annotation is Ellipsis:
         return '...'