Fixup docstring for join_to_timespine in protocol

dbt_semantic_interfaces/protocols/metric.py

@@ -46,7 +46,7 @@ def post_aggregation_measure_reference(self) -> MeasureReference:
     @property
     @abstractmethod
     def join_to_timespine(self) -> bool:
-        """Where the measure should be joined to the timespine."""
+        """If the measure should be joined to the timespine."""
         pass
 
     @property