Fix the CI badge in the README

Author: jessebraham

README.md

@@ -1,6 +1,6 @@
 # espflash
 
-![GitHub Workflow Status](https://img.shields.io/github/workflow/status/esp-rs/espflash/CI?label=CI&labelColor=1C2C2E&logo=github&style=flat-square)
+![GitHub Workflow Status](https://img.shields.io/github/actions/workflow/status/esp-rs/espflash/rust.yml?branch=main&logoColor=1C2C2E&style=flat-square)
 ![Crates.io](https://img.shields.io/crates/l/espflash?labelColor=1C2C2E&style=flat-square)
 [![Matrix](https://img.shields.io/matrix/esp-rs:matrix.org?label=join%20matrix&color=BEC5C9&labelColor=1C2C2E&logo=matrix&style=flat-square)](https://matrix.to/#/#esp-rs:matrix.org)