ci(mergify): upgrade configuration to current format (elastic#18835)

mergify[bot] · herrBez · commit 7e466ca4ba53 · 2026-06-01T17:56:17.000+02:00
diff --git a/.mergify.yml b/.mergify.yml
@@ -1,7 +1,7 @@
 queue_rules:
   - name: default
     merge_method: squash
-    conditions:
+    merge_conditions:
       - check-success=integrations/pr-merge
 
 defaults:
