Fix warnonce bug

Change warnonce to warning_once, which is the correct method.

src/graphnet/models/graphs/edges/edges.py

@@ -27,7 +27,7 @@ def forward(self, graph: Data) -> Data:
             graph: a graph with edges
         """
         if graph.edge_index is not None:
-            self.warnonce(
+            self.warning_once(
                 "GraphBuilder received graph with pre-existing "
                 "structure. Will overwrite."
             )