ci(mergify): upgrade configuration to current format

mergify[bot] · web-flow · commit 16192a03344f · 2026-06-17T02:25:44.000Z
diff --git a/.github/mergify.yml b/.github/mergify.yml
@@ -1,4 +1,3 @@
----
 pull_request_rules:
   - name: Auto-merge dependabot updates when checks pass
     conditions:
@@ -33,4 +32,4 @@ pull_request_rules:
     actions:
       assign:
         add_users:
-          - "{{author}}"
+          - "{{ author }}"
