Add codecov to ci

Author: ofekshenawa

README.md

@@ -3,6 +3,7 @@
 [![build workflow](https://github.com/redis/go-redis/actions/workflows/build.yml/badge.svg)](https://github.com/redis/go-redis/actions)
 [![PkgGoDev](https://pkg.go.dev/badge/github.com/redis/go-redis/v9)](https://pkg.go.dev/github.com/redis/go-redis/v9?tab=doc)
 [![Documentation](https://img.shields.io/badge/redis-documentation-informational)](https://redis.uptrace.dev/)
+[![codecov](https://codecov.io/github/redis/go-redis/graph/badge.svg?token=tsrCZKuSSw)](https://codecov.io/github/redis/go-redis)
 [![Chat](https://discordapp.com/api/guilds/752070105847955518/widget.png)](https://discord.gg/rWtp5Aj)
 
 > go-redis is brought to you by :star: [**uptrace/uptrace**](https://github.com/uptrace/uptrace).