Fix `KeyValuePairAt` memory leak

(cherry picked from commit 1fdfc379b6230b7d3dac4f22c846c45e93cd596d)

modules/mono/glue/collections_glue.cpp

@@ -236,10 +236,8 @@ int32_t godot_icall_Dictionary_KeyValuePairs(Dictionary *ptr, Array **keys, Arra
 }
 
 void godot_icall_Dictionary_KeyValuePairAt(Dictionary *ptr, int index, MonoObject **key, MonoObject **value) {
-	Array *keys = godot_icall_Dictionary_Keys(ptr);
-	Array *values = godot_icall_Dictionary_Values(ptr);
-	*key = GDMonoMarshal::variant_to_mono_object(keys->get(index));
-	*value = GDMonoMarshal::variant_to_mono_object(values->get(index));
+	*key = GDMonoMarshal::variant_to_mono_object(ptr->get_key_at_index(index));
+	*value = GDMonoMarshal::variant_to_mono_object(ptr->get_value_at_index(index));
 }
 
 void godot_icall_Dictionary_Add(Dictionary *ptr, MonoObject *key, MonoObject *value) {