fix pylint E1120 error.

Author: GdoongMathew

src/lightning/pytorch/utilities/model_helpers.py

@@ -15,7 +15,7 @@
 import inspect
 import logging
 import os
-from typing import TYPE_CHECKING, Any, Callable, Generic, Optional, TypeVar
+from typing import TYPE_CHECKING, Any, Callable, Optional, TypeVar
 
 from lightning_utilities.core.imports import RequirementCache
 from torch import nn
@@ -104,14 +104,15 @@ def _check_mixed_imports(instance: object) -> None:
 _R_co = TypeVar("_R_co", covariant=True)  # return type of the decorated method
 
 
-class _restricted_classmethod_impl(Generic[_T, _R_co, _P]):
+class _restricted_classmethod_impl(classmethod):
     """Drop-in replacement for @classmethod, but raises an exception when the decorated method is called on an instance
     instead of a class type."""
 
     def __init__(self, method: Callable[Concatenate[type[_T], _P], _R_co]) -> None:
+        super().__init__(method)
         self.method = method
 
-    def __get__(self, instance: Optional[_T], cls: type[_T]) -> Callable[_P, _R_co]:
+    def __get__(self, instance: Optional[_T], cls: type[_T] | None = None) -> Callable[_P, _R_co]:
         # The wrapper ensures that the method can be inspected, but not called on an instance
         @functools.wraps(self.method)
         def wrapper(*args: Any, **kwargs: Any) -> _R_co: