Fix type check for non-standard schedulers in horovod (#14215)

Author: awaelchli

src/pytorch_lightning/CHANGELOG.md

@@ -62,6 +62,12 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Removed the experimental `pytorch_lightning.utiltiies.meta` functions in favor of built-in https://github.com/pytorch/torchdistx support ([#13868](https://github.com/Lightning-AI/lightning/pull/13868))
 
 
+### Fixed
+
+- Fixed an assertion error when using a `ReduceOnPlateau` scheduler with the Horovod strategy ([#14215](https://github.com/Lightning-AI/lightning/pull/14215))
+
+
+
 ## [1.7.2] - 2022-08-17
 
 ### Added

src/pytorch_lightning/strategies/horovod.py

@@ -31,7 +31,6 @@
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.imports import _HOROVOD_AVAILABLE
 from pytorch_lightning.utilities.rank_zero import rank_zero_only
-from pytorch_lightning.utilities.types import _LRScheduler
 
 if _HOROVOD_AVAILABLE:
     import horovod.torch as hvd
@@ -114,8 +113,8 @@ def _unpack_lightning_optimizer(opt: Optimizer) -> Optimizer:
         lr_scheduler_configs = self.lr_scheduler_configs
         for config in lr_scheduler_configs:
             scheduler = config.scheduler
-            assert isinstance(scheduler, _LRScheduler)
-            scheduler.base_lrs = [lr * self.world_size for lr in scheduler.base_lrs]
+            if hasattr(scheduler, "base_lrs"):
+                scheduler.base_lrs = [lr * self.world_size for lr in scheduler.base_lrs]  # type: ignore[union-attr]
 
         assert self.lightning_module is not None
         # Horovod: broadcast parameters & optimizer state to ensure consistent initialization