LightningModule.log_dict: fix type hints for MetricCollection (#18646)

src/lightning/pytorch/core/module.py

@@ -519,7 +519,7 @@ def log(
 
     def log_dict(
         self,
-        dictionary: Mapping[str, _METRIC],
+        dictionary: Union[Mapping[str, _METRIC], MetricCollection],
         prog_bar: bool = False,
         logger: Optional[bool] = None,
         on_step: Optional[bool] = None,
@@ -594,7 +594,9 @@ def log_dict(
             )
         return None
 
-    def _log_dict_through_fabric(self, dictionary: Mapping[str, Any], logger: Optional[bool] = None) -> None:
+    def _log_dict_through_fabric(
+        self, dictionary: Union[Mapping[str, _METRIC], MetricCollection], logger: Optional[bool] = None
+    ) -> None:
         if logger is False:
             # Passing `logger=False` with Fabric does not make much sense because there is no other destination to
             # log to, but we support it in case the original code was written for Trainer use
@@ -606,7 +608,7 @@ def _log_dict_through_fabric(self, dictionary: Mapping[str, Any], logger: Option
             apply_to_collection(value, object, self.__check_allowed, name, value, wrong_dtype=(numbers.Number, Tensor))
 
         assert self._fabric is not None
-        self._fabric.log_dict(metrics=dictionary)
+        self._fabric.log_dict(metrics=dictionary)  # type: ignore[arg-type]
 
     @staticmethod
     def __check_not_nested(value: dict, name: str) -> None: