docs: fix upgrade guide cursor selector

[hiromieguchi802-lab]

Fixes #2460

Updates the upgrade guide CSS snippet to use aria-disabled for non-form elements with role=button.

[vercel]

@hiromieguchi802-lab is attempting to deploy a commit to the Tailwind Labs Team on Vercel.

A member of the Team first needs to authorize it.

[hiromieguchi802-lab]

FYI: the Vercel check currently shows 'Authorization required to deploy' for this fork PR (seems to require a team member to authorize). This change is just a small docs snippet fix.

[hiromieguchi802-lab]

Quick follow-up: the only failing check I can see on this fork PR is Vercel's Authorization required to deploy status.

The change here is limited to the upgrade guide snippet update. If you'd like any wording or example adjusted, I can update the PR.