Reflow work item buttons when constrained

What does this MR do and why?

Fixes a bug where it was possible for the merge request button to overflow the available space.

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• https://gitlab.com/gitlab-org/gitlab/-/issues/512715#note_2330934903

MR acceptance checklist

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Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After
	(no change)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Open an issue, ideally in a project with both a repository and LFS enabled (design feature is available)
2. Change the URL to replace issues with work_items
   1. Alternately, enable work_items_view_preference feature flag, then change the toggle at the top to "ON"
3. Resize to see reflow

Closes #517432 (closed)