ci(mergify): upgrade configuration to current format

Author: mergify[bot]

.mergify.yml

@@ -1,20 +1,19 @@
----
 queue_rules:
   - name: default
-    conditions:
+    queue_conditions:
+      - label=ready-to-merge
+      - '#approved-reviews-by>=1'
+      - status-success~=^Build docs on ubuntu-latest
+      - status-success~=^Build docs on macos-latest
+      - status-success~=docs/readthedocs.org
+    merge_conditions:
       - check-success~=^Build docs on ubuntu-latest
       - check-success~=^Build docs on macos-latest
       - check-success~=docs/readthedocs.org
+    merge_method: rebase
 
 pull_request_rules:
   - name: automatic merge
-    conditions:
-      - label=ready-to-merge
-      - '#approved-reviews-by>=1'
-      - status-success~=^Build docs on ubuntu-latest
-      - status-success~=^Build docs on macos-latest
-      - status-success~=docs/readthedocs.org
+    conditions: []
     actions:
       queue:
-        method: rebase
-        name: default