[BE][Ez]: Fix bad TypeIs conversion (pytorch#138990)

Fixes on TypeIs / TypeGuard conversion error. Follow up to pytorch#133814
Thanks for @ezyang for reminding me to double check the side conditions here.

Pull Request resolved: pytorch#138990
Approved by: https://github.com/malfet

Author: Skylion007

torch/_subclasses/fake_tensor.py

@@ -32,7 +32,7 @@
     TypeVar,
     Union,
 )
-from typing_extensions import Self, TypeIs
+from typing_extensions import Self, TypeGuard, TypeIs
 from weakref import ReferenceType
 
 import torch
@@ -1214,7 +1214,7 @@ def reset_nt_tensor_id_counter(self) -> None:
     # In this case, it's insufficient to test only one FakeTensor: you need
     # to distinguish between our fake tensor and other fake tensors.  That's
     # what this function does.
-    def is_our_fake(self, t: object) -> TypeIs[FakeTensor]:
+    def is_our_fake(self, t: object) -> TypeGuard[FakeTensor]:
         return isinstance(t, FakeTensor) and t.fake_mode is self
 
     # If we should avoid device init. This changes the behavior of various APIs: