Reduce redundant visits in MR settings spec

What does this MR do and why?

Reduce redundant visits in MR settings spec

Restructures the project Merge requests settings feature spec so that every example performs the minimum number of visits required to load the page under test. This removes 7 redundant cross-scope visits flagged by the repeated visits detector and follows the pattern established for the admin general settings specs.

References #600963 (closed)

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Related to #600963 (closed)