Fix `ReduceLROnPlateau` object has no attribute 'get_last_lr'
Author: wasupandceacar
Pull request: yes

# What does this PR do?

Fix bug when setting lr_scheduler to `ReduceLROnPlateau`. When selecting this scheduler, use the optimizer to get the lr.

Refer to [this discussion](https://discuss.pytorch.org/t/shouldnt-reducelronplateau-super-optimizer-in-its-init/89390/2).

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Fixes #23934


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Comments:
_The documentation is not available anymore as the PR was closed or merged._

> Thanks for the fix! Can you run a quick `make style` on your branch?

done