add a mergify rule for preparing next version

.mergify.yml

@@ -11,3 +11,14 @@ pull_request_rules:
     actions:
       merge:
         method: merge
+
+  - name: Automatic merge for Preparing next version
+    conditions:
+      - author = GitHub Action
+      - '#approved-reviews-by >= 1'
+      - check-skipped = "test (16.x)"
+      - check-skipped = "test-prod-node14 / launch-prod"
+      - check-skipped = "test-prod-node16 / launch-prod"
+    actions:
+      merge:
+        method: merge