Update folium/map.py

Co-authored-by: Frank Anema <33519926+Conengmo@users.noreply.github.com>

folium/map.py

@@ -32,7 +32,7 @@ class Evented(MacroElement):
     method using python keyword arguments.
     """
 
-    def on(self, **event_map):
+    def on(self, **event_map: JsCode):
         for event_type, handler in event_map.items():
             self.add_child(EventHandler(event_type, handler))