Actually set GDScript static reference

(cherry picked from commit 0f1da724924fc494bfd316c57757e0e1d7b90143)

modules/gdscript/gdscript_function.cpp

@@ -386,6 +386,8 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 		}
 	}
 
+	static_ref = script;
+
 	String err_text;
 
 #ifdef DEBUG_ENABLED