Merge pull request godotengine#103198 from Naputt1/fix-tween.kill()-isValid()-return-false

Fix `Tween.is_valid()` returning `true` after calling `kill()`

Author: Repiteo

scene/animation/tween.cpp

@@ -212,6 +212,7 @@ void Tween::play() {
 
 void Tween::kill() {
 	running = false; // For the sake of is_running().
+	valid = false;
 	dead = true;
 }