ci: automatically cancel jobs when new commits are pushed

There is no point in keeping multiple jobs running on a pull request
when new commits are pushed. Automatically cancel them to avoid
confusion.

Link: getpatchwork/patchwork@09939ba107bde8
Signed-off-by: Robin Jarry <robin@jarry.cc>

.github/workflows/ci.yml

@@ -9,6 +9,10 @@ on:
       - main
   pull_request:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build:
     runs-on: ubuntu-24.04