refactor(slice): simplify SliceValidationError Error method (#3910)

* Simplify SliceValidationError Error method

* Replace fmt.Fprintf with b.WriteString

---------

Co-authored-by: huangzw <huangzw@hsmap.com>
Co-authored-by: 1911860538 <alxps1911@163.com>

binding/default_validator_benchmark_test.go

@@ -12,11 +12,15 @@ import (
 
 func BenchmarkSliceValidationError(b *testing.B) {
 	const size int = 100
+	e := make(SliceValidationError, size)
+	for j := 0; j < size; j++ {
+		e[j] = errors.New(strconv.Itoa(j))
+	}
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
 	for i := 0; i < b.N; i++ {
-		e := make(SliceValidationError, size)
-		for j := 0; j < size; j++ {
-			e[j] = errors.New(strconv.Itoa(j))
-		}
 		if len(e.Error()) == 0 {
 			b.Errorf("error")
 		}