Class reference: snake_case .gd filenames, _on_*

This is for:
https://github.com/godotengine/godot-docs/issues/6245

doc/classes/Callable.xml

@@ -14,7 +14,7 @@
 		func test():
 		    var callable = Callable(self, "print_args")
 		    callable.call("hello", "world")  # Prints "hello world ".
-		    callable.call(Vector2.UP, 42, callable)  # Prints "(0, -1) 42 Node(Node.gd)::print_args".
+		    callable.call(Vector2.UP, 42, callable)  # Prints "(0, -1) 42 Node(node.gd)::print_args".
 		    callable.call("invalid")  # Invalid call, should have at least 2 arguments.
 		[/gdscript]
 		[csharp]