ci: cancel CI workflow that becomes obsolete after a new commit is pushed in an open PR

Signed-off-by: Konstantinos <konstantinos.kitsios@uzh.ch>

.github/workflows/pr-check.yaml

@@ -13,6 +13,10 @@ on:
       - '**.md'
       - '**.MD'
 
+# If two events are triggered within a short time in the same PR, cancel the run of the oldest event
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
 
 jobs:
   validate-pr: