ReduceLROnPlateau scheduler type check

[alexeykarnachev]

🐛 Bug

Incorrect type check for scheduler of class ReduceLROnPlateau.
https://github.com/PyTorchLightning/pytorch-lightning/blob/bc01b9ac1c0ddf503f83755c00d5541a2679e5b4/pytorch_lightning/trainer/trainer.py#L713

I believe, this check:
isinstance(scheduler, optim.lr_scheduler.ReduceLROnPlateau)

must look like this:
isinstance(scheduler['scheduler'], optim.lr_scheduler.ReduceLROnPlateau)

To Reproduce

Steps to reproduce the behavior:

1. Create a scheduler of type optim.lr_scheduler.ReduceLROnPlateau in the configure_optimizers method of a LightningModule class.
2. Return an optimizer and scheduler from this method. Place them in lists: return [optimizer], [scheduler].
3. Execute the trainer.fit(module).
4. Put a break-point here: https://github.com/PyTorchLightning/pytorch-lightning/blob/bc01b9ac1c0ddf503f83755c00d5541a2679e5b4/pytorch_lightning/trainer/trainer.py#L712
5. Make sure that the condition is never True.

[github-actions]

Hi! thanks for your contribution!, great first issue!

[Borda]

@SkafteNicki could you pls check it? as it comes from your PR :]

[SkafteNicki]

I agree with @alexeykarnachev that this is indeed a bug, that I introduced with the recent rework of the learning rate schedulers. I can send a new PR with the bug fix and include a test for ReduceLROnPlateau schedulers

[Borda]

Thx guys!
@alexeykarnachev minds send fix PR?