Changed URL for a page that was indexed by Googlebot. Will redirect 301 from the old URL to the new one. But what to do with my Sitemap?

I’m planning to change a url for one of my site’s page.

Example:

From: https://www.example.com/old-post-slug

To: https://www.example.com/new-post-slug

The fact is that Google has already indexed the old url: https://www.example.com/old-post-slug

And from these DOC’s, we see that to avoid lose page ranking we should respond with a 301 - Moved permanently from the old URL pointing to the new URL.

https://support.google.com/webmasters/answer/6033049?hl=en

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QUESTION

I get that I should redirect (301) from the old URL to the new one. So when Google re-crawls, it will see that change. But what should be on my Sitemap? The old URL or the new one? Or both?

I tend to think that it would be best to keep only the new url on my Sitemap. But what if Google crawls the new URL before it sees the redirect from the old one? Wouldn’t the new page URL start off as a new page (from Google’s index perspective) with zero ranking points? How does Googlebot handles that? What is the recommended practice?