ci(mergify): upgrade configuration to current format

.mergify.yml

@@ -1,13 +1,14 @@
-pull_request_rules:
-  - name: Automatic merge on approval
-    conditions:
+queue_rules:
+  - name: default
+    queue_conditions:
       - "#approved-reviews-by>=2"
       - check-success=build (stable)
       - check-success=CodeFactor
       - check-success=Rust project
-    actions:
-      queue:
-        method: squash
+    merge_conditions: []
+    merge_method: squash
+
+pull_request_rules:
   - name: automatic update of pull requests where more 5 commits behind
     conditions:
       - "#commits-behind>5"
@@ -17,4 +18,8 @@ pull_request_rules:
     conditions:
       - merged
     actions:
-      delete_head_branch: {}
+      delete_head_branch: {}
+  - name: Automatic merge on approval
+    conditions: []
+    actions:
+      queue: