fix typos in datamodule (#8949)

Co-authored-by: Knarik Mheryan <[email protected]>

Author: Knarik1

pytorch_lightning/core/datamodule.py

@@ -184,7 +184,7 @@ def dims(self, d):
         rank_zero_deprecation("DataModule property `dims` was deprecated in v1.5 and will be removed in v1.7.")
         self._dims = d
 
-    def size(self, dim=None) -> Union[Tuple, int]:
+    def size(self, dim=None) -> Union[Tuple, List[Tuple]]:
         """
         Return the dimension of each input either as a tuple or list of tuples. You can index this
         just as you would with a torch tensor.