Add GHA CI autocancel (#208)

Author: trsvchn

.github/workflows/ci.yml

@@ -7,6 +7,11 @@ on:
   schedule:
     - cron: '0 0 * * *'
 
+concurrency:
+  # <workflow_name>-<branch_name>-<true || commit_sha (if branch is protected)>
+  group: ci-${{ github.ref_name }}-${{ !(github.ref_protected) || github.sha }}
+  cancel-in-progress: true
+
 jobs:
   tests:
     runs-on: ${{ matrix.os }}