[Net] Fix Multiplayer Bomber custom spawner.

Needed starting beta11 (Godot GH-71129).

networking/multiplayer_bomber/bomb_spawner.gd

@@ -1,6 +1,10 @@
 extends MultiplayerSpawner
 
-func _spawn_custom(data):
+func _init():
+	spawn_function = _spawn_bomb
+
+
+func _spawn_bomb(data):
 	if data.size() != 2 or typeof(data[0]) != TYPE_VECTOR2 or typeof(data[1]) != TYPE_INT:
 		return null
 	var bomb = preload("res://bomb.tscn").instantiate()