Update badge for new workflow
<p align="center">
<a href="https://github.com/gleam-lang/gleam/releases"><img src="https://img.shields.io/github/release/gleam-lang/gleam" alt="GitHub release"></a>
<a href="https://webchat.freenode.net/#gleam-lang"><img src="https://img.shields.io/badge/freenode%20chat-%23gleam--lang-blue" alt="IRC: #gleam-lang on chat.freenode.net"></a>
- <a><img src="https://github.com/gleam-lang/gleam/workflows/Test%20compiler/badge.svg?branch=main"></a>
+ <a><img src="https://github.com/gleam-lang/gleam/workflows/ci/badge.svg?branch=main"></a>
</p>
