Tidy WorkItemActions and update feature specs

What does this MR do and why?

Tidy WorkItemActions (in preparation for adding a new feature to it as part of #398649 (closed)) and update feature specs

Update work item feature specs to follow our UI testing guidelines of using UI text and capybara actions/matchers where possible, for accessibility and readability.

Screenshots or screen recordings

No visual changes

How to set up and validate locally

MR acceptance checklist

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