Update ListboxHelper to adhere to Pajamas style

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What does this MR do and why?

Fixes: #417800 (closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

See !151151 (comment 1911124165).

How to set up and validate locally

1. Visit some of the places this helper is used:
   • project forks page http://gdk.test:3000/gitlab-org/gitlab-test/-/forks
   • project starrers page http://gdk.test:3000/gitlab-org/gitlab-test/-/starrers
2. Ensure the dropdown looks correct. Ideally, load the page with JavaScript disabled, since the markup this changes is completely replaced by Vue components once JS is executed.
3. Bonus points: compare DOM structure with a real listbox (just the button and parent element, not the menu).

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changed title from Draft: Update Bt to Pajamas::ButtonComponent to Draft: Update to Pajamas::ButtonComponent

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added 1 commit

• 015ce4e8 - Add link_bt_to for migration

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	3 Warnings
	This merge request does not refer to an existing milestone.
	You've made some app changes, but didn't add any tests. That's OK as long as you're refactoring existing code, but please consider adding any of the maintenancepipelines, maintenancerefactor, maintenanceworkflow, documentation, QA labels.
	Labels missing: please ask a reviewer or maintainer to add frontend, backend to this merge request.

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Category	Reviewer	Maintainer
backend	@jon_jenkins (UTC-5)	@hustewart (UTC-4)
frontend	@thomasrandolph (UTC-6)	@anna_vovchenko (UTC+3)

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requested review from @jannik_lehmann

Thanks for your contribution @sbin64 !

I'm not sure in this case if this is really what we need. If I look at the changes in this MR, this button is actually styled as a link and therefore is one of the exceptions described in: &8153

before changes	after changes

I would recommend to close this MR, and to close: #417901 (closed) leaving a comment that this button is styled as a link and therefore should be left as is. What do you think?

removed review request for @jannik_lehmann