Limit concurrency of our test workflow
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 17d03d3eef..dfd6a8e381 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -1,4 +1,7 @@
 name: Tests
+concurrency:
+  group: ${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
 
 on:
   push:

This seems to be useful to reduce our CI times (e.g pushing 2 commits one after another would block the last commit, since the workflows would be allocated by the first commit. This is making the second cancel the first). See [see the documentation](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#example-using-a-fallback-value) for more details.