Apply suggestion from @alejoe91

Author: alejoe91

src/spikeinterface/curation/remove_redundant.py

@@ -134,7 +134,7 @@ def remove_redundant_units(
 
 
 def find_redundant_units(
-    sorting, delta_time: float = 0.4, agreement_threshold: float = 0.2, duplicate_threshold: float = 0.8
+    sorting: BaseSorting, delta_time: float = 0.4, agreement_threshold: float = 0.2, duplicate_threshold: float = 0.8
 ) -> list[tuple[int, int]]:
     """
     Finds redundant or duplicate units by comparing the sorting output with itself.