Add CI concurrency group (#319)

Author: leighmcculloch

.github/workflows/rust.yml

@@ -5,6 +5,10 @@ on:
     branches: [main, dev]
   pull_request:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref_protected == 'true' && github.sha || github.ref }}
+  cancel-in-progress: true
+
 env:
   MINIMUM_RUST_VERSION: 1.74.0