Actually actually fix mypy typing errors

src/traccuracy/_tracking_graph.py

@@ -426,7 +426,7 @@ def set_flag_on_all_nodes(self, flag: NodeAttr, value: bool = True):
             self.nodes_by_flag[flag] = set()
 
     def set_flag_on_edge(
-        self, _id: tuple[Hashable], flag: EdgeAttr, value: bool = True
+        self, _id: tuple[Hashable, Hashable], flag: EdgeAttr, value: bool = True
     ):
         """Set an attribute flag for an edge.
         If the flag already exists, the existing value will be overwritten.