mergify: replace queue action for queue_rules (#5517)

Force merging as tests won't pass before a 9.x release is available.

Author: v1v

.mergify.yml

@@ -1,5 +1,6 @@
 queue_rules:
   - name: default
+    merge_method: squash
     conditions:
       - check-success=fleet-ci/pr-merge
 pull_request_rules:
@@ -85,7 +86,6 @@ pull_request_rules:
       - "#approved-reviews-by>=1"
     actions:
       queue:
-        method: squash
         name: default
   - name: delete upstream branch with changes on ^.mergify.yml that has been merged or closed
     conditions: