Change "Merge when ready" text to "Enqueue" or "Add to merge queue"

I have a PR with all checks passing, but it shows "Merge when ready"

In other tools "Merge when ready" means "add to a queue when PR checks pass".

Here, it means "it will merge when it CI passes in the merge queue once you press this button enqueue it", which is a quite complex concept.

Can it be named "Add to a queue"?

首先在 gh-stack 仓库中定位 "Merge when ready" 文本，并阅读周围的代码，以了解该标签在哪里定义。将措辞改为所要求的队列术语，然后验证显示的操作传达的是将 pull request 加入队列，而不是立即合并。

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