fix test compatibility as AdamW became subclass of Adam (#20574)

Co-authored-by: Haifeng Jin <[email protected]>

Author: haifeng-jin

tests/tests_pytorch/callbacks/test_lr_monitor.py

@@ -548,10 +548,10 @@ def finetune_function(self, pl_module, epoch: int, optimizer):
             """Called when the epoch begins."""
             if epoch == 1 and isinstance(optimizer, torch.optim.SGD):
                 self.unfreeze_and_add_param_group(pl_module.backbone[0], optimizer, lr=0.1)
-            if epoch == 2 and isinstance(optimizer, torch.optim.Adam):
+            if epoch == 2 and type(optimizer) is torch.optim.Adam:
                 self.unfreeze_and_add_param_group(pl_module.layer, optimizer, lr=0.1)
 
-            if epoch == 3 and isinstance(optimizer, torch.optim.Adam):
+            if epoch == 3 and type(optimizer) is torch.optim.Adam:
                 assert len(optimizer.param_groups) == 2
                 self.unfreeze_and_add_param_group(pl_module.backbone[1], optimizer, lr=0.1)
                 assert len(optimizer.param_groups) == 3