Fix SCRIPT ERROR/ERROR/WARNING on test output

Also "fixing" some GDScript completion tests which
where named wrongly.

modules/gdscript/tests/scripts/completion/get_node/member_scene/class_member_scene.gd

@@ -1,6 +1,6 @@
 extends Node
 
-var test = $A
+@onready var test = $A
 
 func a():
     test.➡

modules/gdscript/tests/scripts/completion/get_node/member_scene/native_member_scene.gd

@@ -1,6 +1,6 @@
 extends Node
 
-var test = $AnimationPlayer
+@onready var test = $AnimationPlayer
 
 func a():
     test.➡