Remove codecov badge (#29950)

It's been broken since the migration to actions, so lets remove it.

Author: silverwind

README.md

@@ -2,7 +2,6 @@
 
 [![](https://github.com/go-gitea/gitea/actions/workflows/release-nightly.yml/badge.svg?branch=main)](https://github.com/go-gitea/gitea/actions/workflows/release-nightly.yml?query=branch%3Amain "Release Nightly")
 [![](https://img.shields.io/discord/322538954119184384.svg?logo=discord&logoColor=white&label=Discord&color=5865F2)](https://discord.gg/Gitea "Join the Discord chat at https://discord.gg/Gitea")
-[![](https://codecov.io/gh/go-gitea/gitea/branch/main/graph/badge.svg)](https://app.codecov.io/gh/go-gitea/gitea "Codecov")
 [![](https://goreportcard.com/badge/code.gitea.io/gitea)](https://goreportcard.com/report/code.gitea.io/gitea "Go Report Card")
 [![](https://pkg.go.dev/badge/code.gitea.io/gitea?status.svg)](https://pkg.go.dev/code.gitea.io/gitea "GoDoc")
 [![](https://img.shields.io/github/release/go-gitea/gitea.svg)](https://github.com/go-gitea/gitea/releases/latest "GitHub release")

README_ZH.md

@@ -2,7 +2,6 @@
 
 [![](https://github.com/go-gitea/gitea/actions/workflows/release-nightly.yml/badge.svg?branch=main)](https://github.com/go-gitea/gitea/actions/workflows/release-nightly.yml?query=branch%3Amain "Release Nightly")
 [![](https://img.shields.io/discord/322538954119184384.svg?logo=discord&logoColor=white&label=Discord&color=5865F2)](https://discord.gg/Gitea "Join the Discord chat at https://discord.gg/Gitea")
-[![](https://codecov.io/gh/go-gitea/gitea/branch/main/graph/badge.svg)](https://app.codecov.io/gh/go-gitea/gitea "Codecov")
 [![](https://goreportcard.com/badge/code.gitea.io/gitea)](https://goreportcard.com/report/code.gitea.io/gitea "Go Report Card")
 [![](https://pkg.go.dev/badge/code.gitea.io/gitea?status.svg)](https://pkg.go.dev/code.gitea.io/gitea "GoDoc")
 [![](https://img.shields.io/github/release/go-gitea/gitea.svg)](https://github.com/go-gitea/gitea/releases/latest "GitHub release")