ci(mergify): upgrade configuration to current format

mergify[bot] · web-flow · commit 24c18ac14400 · 2026-04-20T13:10:48.000Z
diff --git a/.mergify.yml b/.mergify.yml
@@ -1,5 +1 @@
-pull_request_rules:
-  - name: delete head branch after merge
-    conditions: []
-    actions:
-      delete_head_branch: {}
+{}
