fix "conversion from int to string yields a string of one rune" `go vet` error
fix "conversion from int to string yields a string of one rune" `go vet` error

osc/osc_test.go:157:54: conversion from int to string yields a string of one rune

I found some context here: https://github.com/golang/go/issues/32479

hypebeast/go-osc