github: switch to merge-queues

.github/workflows/test.yml

@@ -1,6 +1,7 @@
 name: "Test"
 on:
   pull_request:
+  merge_group:
   push:
     branches:
       - master

.mergify.yml

@@ -1,16 +0,0 @@
-queue_rules:
-  - name: default
-    merge_conditions:
-      - check-success=buildbot/nix-build
-      - check-success=tests (ubuntu-latest, stable)
-      - check-success=tests (ubuntu-latest, latest)
-      - check-success=tests (ubuntu-latest, bash4)
-    batch_size: 5
-    merge_method: rebase
-pull_request_rules:
-  - name: merge using the merge queue
-    conditions:
-      - base=master
-      - label~=merge-queue|dependencies
-    actions:
-      queue: {}