Fix AnimationLibrary loading

Author: KoBeWi

scene/animation/animation_mixer.cpp

@@ -81,9 +81,8 @@ bool AnimationMixer::_set(const StringName &p_name, const Variant &p_value) {
 		List<Variant> keys;
 		d.get_key_list(&keys);
 		for (const Variant &K : keys) {
-			StringName lib_name = K;
-			Ref<AnimationLibrary> lib = d[lib_name];
-			add_animation_library(lib_name, lib);
+			Ref<AnimationLibrary> lib = d[K];
+			add_animation_library(K, lib);
 		}
 		emit_signal(SNAME("animation_libraries_updated"));