fix: finalise returns the whole BatchRequestContent

Author: George Garber

src/msgraph_core/requests/batch_request_content.py

@@ -125,7 +125,7 @@ def finalize(self):
         Finalizes the batch request content.
         """
         self.is_finalized = True
-        return self._requests
+        return self
 
     def _request_by_id(self, request_id: str) -> Optional[BatchRequestItem]:
         """