LightningCLI fails to recognize custom Callback due to mixed import styles

[NikStaBurd]

Bug description

I implemented a custom PyTorch Lightning Callback and passed it to the Trainer via LightningCLI. However, I encountered an error where my callback was not recognized as an instance of Callback inside _validate_callbacks_list().

After debugging, I found that the issue stems from _check_mixed_imports() in lightning/pytorch/utilities/model_helpers.py, which does not correctly detect mixed imports when using lightning.pytorch vs pytorch_lightning.

The Studio Template can be found here: https://lightning.ai/acme-ai/studios/lightningcli-fails-to-recognize-custom-callback-due-to-mixed-import-styles~01hpygektnhxpn0tgm1jk6z485

What version are you seeing the problem on?

v2.5

How to reproduce the bug

import torch
from lightning.pytorch.demos.boring_classes import BoringModel as BoringLightningModule
from lightning.pytorch.demos.dummy_data import DummyDataModule as DummyDatamodule

from lightning.pytorch.cli import LightningCLI    # New import syntax
from pytorch_lightning.callbacks import Callback  # Old import syntax


class MyCallback(Callback):
    def __init__(self):
        super().__init__()
    # More code...


class MyCLI(LightningCLI):
    def add_arguments_to_parser(self, parser):
        super().add_arguments_to_parser(parser)
        parser.add_optimizer_args(torch.optim.SGD)

def cli_main():
    return MyCLI(
        BoringLightningModule,
        DummyDatamodule,
        trainer_defaults={"callbacks": [MyCallback]}
    )

if __name__ == "__main__":
    torch.set_float32_matmul_precision("medium")
    cli = cli_main()

Error messages and logs

  File "/opt/conda/lib/python3.11/site-packages/lightning/pytorch/trainer/connectors/callback_connector.py", line 228, in _validate_callbacks_list
    stateful_callbacks = [cb for cb in callbacks if is_overridden("state_dict", instance=cb)]
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/conda/lib/python3.11/site-packages/lightning/pytorch/utilities/model_helpers.py", line 42, in is_overridden
    raise ValueError("Expected a parent")
ValueError: Expected a parent```


### Environment

<details>
  <summary>Current environment</summary>

#- PyTorch Lightning Version (e.g., 2.5.0):
#- PyTorch Version (e.g., 2.5):
#- Python version (e.g., 3.12):
#- OS (e.g., Linux):
#- CUDA/cuDNN version:
#- GPU models and configuration:
#- How you installed Lightning(conda, pip, source):

</details>


### More info

_No response_