ci: disable Mergify interactive queue controls in PR comments

Motivation:
Rendered task-list checkboxes in the Merge Queue status comment could be
clicked accidentally by reviewers, triggering unexpected merges before
the required approval count was met.

Design Choices:
Set queue_controls_comment to false in the merge_queue block of
.mergify.yml to disable rendering these interactive controls.

Benefits:
Prevents accidental manual queueing and merging of pull requests while
allowing automated queues like Dependabot to work normally.

Author: okurz

.mergify.yml

@@ -1,3 +1,8 @@
+---
+merge_queue:
+  status_comments: none
+  queue_controls_comment: false
+
 pull_request_rules:
   - name: automatic merge
     conditions: