ci(mergify): upgrade configuration to current format

Author: mergify[bot]

.github/mergify.yml

@@ -65,8 +65,8 @@ pull_request_rules:
   - name: Delete the PR branch and remove label after merge/close
     conditions:
       - or:
-        - merged
-        - closed
+          - merged
+          - closed
     actions:
       delete_head_branch: {}
       label:
@@ -80,4 +80,13 @@ pull_request_rules:
       - author=scala-steward
     actions:
       label:
-        add: [ "type:updates" ]
+        add: ["type:updates"]
+priority_rules:
+  - name: priority for queue `default`
+    conditions:
+      - queue-name=default
+    priority: 2500
+  - name: priority for queue `rebase`
+    conditions:
+      - queue-name=rebase
+    priority: 2250