Fix warnonce

Change warnonce to warning_once which is the correct method.

src/graphnet/models/graphs/graph_definition.py

@@ -116,7 +116,7 @@ def forward(  # type: ignore
         if self._edge_definition is not None:
             graph = self._edge_definition(graph)
         else:
-            self.warnonce(
+            self.warning_once(
                 "No EdgeDefinition provided. Graphs will not have edges defined!"
             )
 
@@ -252,7 +252,7 @@ def _add_features_individually(
             if feature not in ["x"]:  # reserved for node features.
                 graph[feature] = graph.x[:, index].detach()
             else:
-                self.warnonce(
+                self.warning_once(
                     """Cannot assign graph['x']. This field is reserved for node features. Please rename your input feature."""
                 )
         return graph