Fix optimizers overloads typing annotation (#10069)

Author: carmocca

pytorch_lightning/core/lightning.py

@@ -130,6 +130,12 @@ def optimizers(self, use_pl_optimizer: Literal[True] = True) -> Union[LightningO
     def optimizers(self, use_pl_optimizer: Literal[False]) -> Union[Optimizer, List[Optimizer]]:
         ...
 
+    @overload
+    def optimizers(
+        self, use_pl_optimizer: bool
+    ) -> Union[Optimizer, LightningOptimizer, List[Optimizer], List[LightningOptimizer]]:
+        ...
+
     def optimizers(
         self, use_pl_optimizer: bool = True
     ) -> Union[Optimizer, LightningOptimizer, List[Optimizer], List[LightningOptimizer]]: