json: fix json decode with sumtype of multi array type (#14035)

vlib/json/json_decode_with_sumtype_test.v

@@ -1,13 +1,21 @@
 import json
 
-type Test = []string | string
+type Test = []bool | []int | []string | string
 
 struct Some {
 	t Test
 }
 
 fn test_json_decode_with_sumtype() ? {
-	v := json.decode(Some, '{"t": ["string", "string2"]}') ?
-	println(v)
-	assert '$v.t' == "Test(['string', 'string2'])"
+	v1 := json.decode(Some, '{"t": ["string", "string2"]}') ?
+	println(v1)
+	assert v1.t == Test(['string', 'string2'])
+
+	v2 := json.decode(Some, '{"t": [11, 22]}') ?
+	println(v2)
+	assert v2.t == Test([11, 22])
+
+	v3 := json.decode(Some, '{"t": [true, false]}') ?
+	println(v3)
+	assert v3.t == Test([true, false])
 }