Fix get_data_derived_from

`obj in v.derived_from` uses equality (==) rather than identity (is).

eitprocessing/datahandling/datacollection.py

@@ -97,7 +97,7 @@ def get_loaded_data(self) -> dict[str, V]:
 
     def get_data_derived_from(self, obj: V) -> dict[str, V]:
         """Return all data that was derived from a specific source."""
-        return {k: v for k, v in self.items() if obj in v.derived_from}
+        return {k: v for k, v in self.items() if any(obj is item for item in v.derived_from)}
 
     def get_derived_data(self) -> dict[str, V]:
         """Return all data that was derived from any source."""