Add concurrency limit in CI (#265)

With this change we'll cancel in-progress workflows when new code is
pushed.

Author: lookback-hugotunius

.github/workflows/cargo.yml

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

.github/workflows/grcov.yml

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