only run one build per branch at a time

Author: iCodeSometime

.github/workflows/test.yml

@@ -6,6 +6,10 @@ on:
   pull_request:
     branches: ["release"]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 env:
   CARGO_TERM_COLOR: always