Fix Actions badge (#897)

Author: atouchet

README.md

@@ -1,7 +1,7 @@
 [![crates.io](https://img.shields.io/crates/v/chumsky.svg)](https://crates.io/crates/chumsky)
 [![crates.io](https://docs.rs/chumsky/badge.svg)](https://docs.rs/chumsky)
 [![License](https://img.shields.io/crates/l/chumsky.svg)](https://github.com/zesterer/chumsky)
-[![actions-badge](https://github.com/zesterer/chumsky/workflows/Rust/badge.svg?branch=master)](https://github.com/zesterer/chumsky/actions)
+[![actions-badge](https://github.com/zesterer/chumsky/actions/workflows/rust.yml/badge.svg)](https://github.com/zesterer/chumsky/actions)
 
 Chumsky is a parser library for Rust that makes writing expressive, high-performance parsers easy.