x.json2.decoder2: include missing test for #22730 (#23051)

vlib/x/json2/decoder2/tests/json_sumtype_test.v

@@ -28,6 +28,21 @@ pub struct Dog {
 
 type Sum = int | string | bool | []string
 
+type StructSumTypes = Stru | Stru2
+
+pub struct Stru {
+	val  int
+	val2 string
+	val3 Stru2
+	val4 int
+	val5 int
+}
+
+pub struct Stru2 {
+	a     int
+	steak string
+}
+
 fn test_simple_sum_type() {
 	assert json.decode[Sum]('1')! == Sum(1)
 
@@ -78,4 +93,7 @@ fn test_sum_type_struct() {
 	assert json.decode[Animal]('{"cat_name": "Tom"}')! == Animal(Cat{'Tom'})
 	assert json.decode[Animal]('{"dog_name": "Rex"}')! == Animal(Cat{''})
 	assert json.decode[Animal]('{"dog_name": "Rex", "_type": "Dog"}')! == Animal(Dog{'Rex'})
+
+	// struct sumtype in random order
+	assert json.decode[StructSumTypes]('{"_type": "Stru", "val": 1, "val2": "lala", "val3": {"a": 2, "steak": "leleu"}, "val4": 2147483000, "val5": 2147483000}')! == StructSumTypes(Stru{1, 'lala', Stru2{2, 'leleu'}, 2147483000, 2147483000})
 }