Fix typo 'wether' (#15710)

Author: dymil

docs/source-pytorch/starter/lightning_lite.rst

@@ -169,7 +169,7 @@ You can also easily use distributed collectives if required.
     # The index of the current node.
     lite.node_rank
 
-    # Wether this global rank is rank zero.
+    # Whether this global rank is rank zero.
     if lite.is_global_zero:
         # do something on rank 0
         ...

src/lightning_lite/lite.py

@@ -135,7 +135,7 @@ def world_size(self) -> int:
 
     @property
     def is_global_zero(self) -> bool:
-        """Wether this rank is rank zero."""
+        """Whether this rank is rank zero."""
         return self._strategy.is_global_zero
 
     def run(self, *args: Any, **kwargs: Any) -> Any: