mergify: replace queue action for queue_rules (#3891)

Force merging as it tests won't pass without a 9.x release

.mergify.yml

@@ -1,5 +1,6 @@
 queue_rules:
   - name: default
+    merge_method: squash
     conditions:
       - check-success=fleet-server/pr-merge
 
@@ -84,7 +85,6 @@ pull_request_rules:
         type: APPROVE
         message: Automatically approving mergify
       queue:
-        method: squash
         name: default
   - name: automatic merge when CI passes and the file dev-tools/integration/.env is modified.
     conditions:
@@ -96,7 +96,6 @@ pull_request_rules:
         type: APPROVE
         message: Automatically approving mergify
       queue:
-        method: squash
         name: default
   - name: delete upstream branch with changes on dev-tools/integration/.env or .go-version after merging/closing it
     conditions: