cancel running ongoing CI runs upon new push

Author: boriskaus

.github/workflows/CI.yml

@@ -6,6 +6,12 @@ on:
     branches:
       - main
     tags: '*'
+
+# Cancel redundant CI tests automatically
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+  
 jobs:
   run_tests:
     name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }} - ${{ github.event_name }}