Remove Unnecessary aria-hidden from Disclosure

Description

aria-hidden attribute is improperly used on the disclosure dropdown group header, which makes it inaccessible to assistive technology.

See GitLab Issue for context

Figma file

View design specs in Figma →

Checklist

Make sure the following are completed before closing the issue:

1. Assign the correct component label to this issue.
2. Create an MR with the additions or updates needed.
3. Be sure to get your MR reviewed by a [FE/UX Foundations designer][foundations-team].
4. When applicable, create an [MR in Pajamas][pajamas-mr] to update the demos. If you do not have capacity to complete the demos, [create an issue in Pajamas][pajamas-issue] and bring the issue to your team planning session for prioritization and scheduling. Mark the issue as related to this one.
5. When applicable, [create an MR in Pajamas][pajamas-mr] to update the component status.
6. When applicable, [create an issue in Pajamas][pajamas-issue] using the ["Component Documentation"][pajamas-component-documentation-template] issue template to update guidelines. Ping a designer on your team for awareness and bring the issue to your team planning meeting for prioritization and scheduling.
7. When applicable, [create an issue in Pajamas][pajamas-issue] using the ["Figma update"][pajamas-figma-update-template] issue template to update the Figma UI Kit. Ping a designer on your team for awareness and bring the issue to your team planning meeting for prioritization and scheduling.
8. When introducing a major or breaking change, communicate the changes within the [Engineering Week in Review][eng-week-in-review-doc].
9. 🎉 Congrats, you made it! You can now close this issue.

[foundations-team]: https://about.gitlab.com/company/team/?department=fe-ux-foundations-team [pajamas-mr]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/new [pajamas-issue]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues/new [pajamas-component-documentation-template]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues/new?issuable_template=Component%20documentation [pajamas-figma-update-template]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues/new?issuable_template=Figma%20update [component-lifecycle]: https://design.gitlab.com/get-started/lifecycle [adding-components]: https://gitlab.com/gitlab-org/gitlab-ui/-/blob/main/doc/contributing/adding_components.md [adding-css]: https://gitlab.com/gitlab-org/gitlab-ui/-/blob/main/doc/contributing/adding_css.md [breaking-changes]: https://gitlab.com/gitlab-org/gitlab-ui/-/blob/main/doc/contributing/breaking_changes_to_components.md [eng-week-in-review-doc]: https://docs.google.com/document/d/1JBdCl3MAOSdlgq3kzzRmtzTsFWsTIQ9iQg0RHhMht6E/edit