ci(mergify): upgrade configuration to current format (#212)

Co-authored-by: Mergify <37929162+mergify[bot]@users.noreply.github.com>

.mergify.yml

@@ -1,23 +1,23 @@
 queue_rules:
   - name: automerge
-    conditions:
-      - check-success=Deprecation_Messages_and_Coverage (3.8)
-
-pull_request_rules:
-  - name: automatic merge on CI success and review
-    conditions:
+    queue_conditions:
       - check-success=Deprecation_Messages_and_Coverage (3.8)
       - "#approved-reviews-by>=1"
       - label=automerge
       - label!=on hold
-    actions:
-      queue:
-        name: automerge
-        method: squash
+    merge_conditions:
+      - check-success=Deprecation_Messages_and_Coverage (3.8)
+    merge_method: squash
+
+pull_request_rules:
   - name: backport
     conditions:
       - label=stable backport potential
     actions:
       backport:
         branches:
           - stable/0.3
+  - name: refactored queue action rule
+    conditions: []
+    actions:
+      queue: