Fix TypeError in configure_optimizers when running with ReduceLROnPlateau (#20471)

* fix TypeError in configure_optimizers

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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---------

Co-authored-by: Lukas Salchow <sachowlukas@gmail.com>
Co-authored-by: Luca Antiga <luca.antiga@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 4 people

src/lightning/pytorch/utilities/types.py

@@ -104,18 +104,25 @@ class LRSchedulerConfigType(TypedDict, total=False):
     strict: bool
 
 
-class OptimizerLRSchedulerConfig(TypedDict):
+class OptimizerConfigDict(TypedDict):
     optimizer: Optimizer
-    lr_scheduler: NotRequired[Union[LRSchedulerTypeUnion, LRSchedulerConfigType]]
+
+
+class OptimizerLRSchedulerConfigDict(TypedDict):
+    optimizer: Optimizer
+    lr_scheduler: Union[LRSchedulerTypeUnion, LRSchedulerConfigType]
+    monitor: NotRequired[str]
 
 
 OptimizerLRScheduler = Optional[
     Union[
         Optimizer,
         Sequence[Optimizer],
         tuple[Sequence[Optimizer], Sequence[Union[LRSchedulerTypeUnion, LRSchedulerConfig]]],
-        OptimizerLRSchedulerConfig,
-        Sequence[OptimizerLRSchedulerConfig],
+        OptimizerConfigDict,
+        OptimizerLRSchedulerConfigDict,
+        Sequence[OptimizerConfigDict],
+        Sequence[OptimizerLRSchedulerConfigDict],
     ]
 ]