Fix incorrect instructions on the document for "Merge request approvals"

What does this MR do and why?

While guiding a customer through the process of requiring approval for merge requests, I noticed an incorrect points in the details on this page.
Specifically, the name of the hierarchy of the menu for making the setting is different from the actual screen in gitlab.com as of 2022-12-23 .

Screenshots or screen recordings

this is screen in gitlab.com as of 2022-12-23 .

How to set up and validate locally

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.