func s2s use deprecated code in golang 1.20

[tvojacek]

Same problem has been solved in fasthttp in valyala/fasthttp#1481
Original code:
func s2b(s string) (b []byte) {
strh := (*reflect.StringHeader)(unsafe.Pointer(&s))
sh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
sh.Data = strh.Data
sh.Len = strh.Len
sh.Cap = strh.Len
return b
}

Was replaced in b2s_new.go
// s2b converts string to a byte slice without memory allocation.
func s2b(s string) []byte {
return unsafe.Slice(unsafe.StringData(s), len(s))
}