CI: cancel other builds if others are building for the same commit too (this happens when a commit is tagged)

.github/workflows/CI.yml

@@ -5,6 +5,9 @@ on: [push, pull_request]
 jobs:
   CI:
     runs-on: ubuntu-latest
+    concurrency:
+      group: ${{ github.sha }}
+      cancel-in-progress: true
     steps:
     - name: Checkout
       uses: actions/checkout@v3