[ci]: enable merge queues (#5994)

Required for merge queues, so we have some tests that run in the merge
queue:
https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-a-merge-queue#triggering-merge-group-checks-with-github-actions

.github/workflows/format.yml

@@ -6,6 +6,7 @@ on:
       - master
       - 'feature/**'
       - '*-lcm'
+  merge_group:
 
 jobs:
   ocaml-format:

.github/workflows/main.yml

@@ -6,6 +6,7 @@ on:
   schedule:
     # run daily, this refreshes the cache
     - cron: "13 2 * * *"
+  merge_group:
 
 concurrency: # On new push, cancel old workflows from the same PR, branch or tag:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}

.github/workflows/other.yml

@@ -6,6 +6,7 @@ on:
   schedule:
     # run daily, this refreshes the cache
     - cron: "13 2 * * *"
+  merge_group:
 
 concurrency: # On new push, cancel old workflows from the same PR, branch or tag:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}

.github/workflows/shellcheck.yaml

@@ -2,6 +2,7 @@ name: ShellCheck
 
 on:
   pull_request:
+  merge_group:
 
 concurrency:  # On new push, cancel old workflows from the same PR, branch or tag:
   group: sc-${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}