chore: add merge queue for pr verify

.github/pull_request_template.md

@@ -0,0 +1,24 @@
+## Summary
+
+- What does this merge request implement?
+- What are the most important pieces of code to review?
+- Other bugs or minor issues you have fixed?
+- Fixes # [...]
+
+## Impact
+
+- [ ] App
+- [ ] Supabase functions
+- [ ] Supabase migration
+- [ ] CI / GitHub
+- [ ] `pubspec.yaml`
+
+## Testing steps
+
+What steps should the reviewer follow to test this change?
+
+## Open points
+
+What do you intend to address later?
+What else is still unclear at the time of writing,
+and needs further discussion before implementing?

.github/workflows/verify.yaml

@@ -2,6 +2,13 @@ name: Verify
 
 on:
   pull_request:
+  merge_group:
+
+# We only care about the latest version: stop old jobs if a new commit is pushed.
+# The fallback on github.ref is for when the workflow is for a merge queue.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
 
 jobs:
   flutter: