ci(mergify): upgrade configuration to current format

mergify[bot] · web-flow · commit 57514c1c4603 · 2026-04-01T21:03:47.000Z
diff --git a/.mergify.yml b/.mergify.yml
@@ -18,8 +18,3 @@ pull_request_rules:
       queue:
         name: default
 
-  - name: Delete head branch after merge
-    conditions:
-      - merged
-    actions:
-      delete_head_branch: {}
