Sprite: Fix inspector not showing changes on "frame" property.

Fixes #6562

(cherry picked from commit 9d67895c7c3801e830d2c6e8c0fdf66f3ffc0893)

scene/2d/sprite.cpp

@@ -214,6 +214,7 @@ void Sprite::set_frame(int p_frame) {
 
 	frame=p_frame;
 
+	_change_notify("frame");
 	emit_signal(SceneStringNames::get_singleton()->frame_changed);
 }