docs: fix badge URLs in README

Author: oxalica

README.md

@@ -1,7 +1,7 @@
 # rust-overlay
 
-[![CI status](https://github.com/oxalica/rust-overlay/workflows/CI/badge.svg)](https://github.com/oxalica/rust-overlay/actions/workflows/ci.yaml)
-[![sync-channels status](https://github.com/oxalica/rust-overlay/workflows/sync-channels/badge.svg)](https://github.com/oxalica/rust-overlay/actions/workflows/sync-channels.yaml)
+[![CI](https://github.com/oxalica/rust-overlay/actions/workflows/ci.yaml/badge.svg)](https://github.com/oxalica/rust-overlay/actions/workflows/ci.yaml)
+[![Sync channels](https://github.com/oxalica/rust-overlay/actions/workflows/sync-channels.yaml/badge.svg)](https://github.com/oxalica/rust-overlay/actions/workflows/sync-channels.yaml)
 
 *Pure and reproducible* packaging of binary distributed rust toolchains.
 A compatible but better replacement for rust overlay of [nixpkgs-mozilla],