Replace the 'project/merge_requests/revert.feature' spinach test with an rspec analog

What does this MR do?

This MR moves all the test from the features/project/merge_requests/revert.feature spinach spec to an rspec analog.

Why was this MR needed?

This is a part of the spinach removal campaign.

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

#23036 (moved)

Edited by username-removed-86853

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