Enable merge queues (#362)

For more details see:

https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-a-merge-queue

Author: llucax

.github/workflows/ci.yaml

@@ -1,6 +1,6 @@
 name: frequenz-sdk-python
 
-on: [pull_request, push, workflow_dispatch]
+on: [merge_group, pull_request, push, workflow_dispatch]
 
 jobs:
   test: