Update eventlog_handler.py

in List_of_columns(self) return a list ,so it should be def list_of_columns(self) -> list: not :def list_of_columns(self) -> dict:

src/eventlog_handler.py

@@ -51,7 +51,7 @@ class Event_handler:
         
             
     
-    def list_of_columns(self) -> dict:
+    def list_of_columns(self) -> list:
         return list(self.df.columns)        
 
     def select_columns(self, case_id:str, timestamp:str, activity:str, resource :str = None) -> dict: