Correct capability for the Experiments page

[rmccue]

What?

Changes the capability for the Experiments page to manage_options

Why?

Fixes #66117

How?

Changes the page registration cap.

Testing Instructions

1. Create a user as an Editor
2. Log in as that user
3. Observe Experiments page before and after

[github-actions]

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[rmccue]

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Fixed!

[rmccue]

I searched beforehand but somehow it didn't show @t-hamano's #56359, so request whoever merges props them as well :)