Roles in RolePickerMenu are not discoverable without scroll wheel or touchpad

<!-- Please only use this template for submitting accessibility issues. This is a new feature area for Grafana that we want to improve. We have long way to go to really improve accessibility and would like your help to know where to start. --> **Steps to reproduce**: 1. Have a setup where you use only your mouse and keyboard, and you have the scroll wheel disabled. 2. Go to `/admin/users` with a user who can assign roles in an org. 3. Click on a role field which opens the RolePickerMenu 4. Try to scan through the available roles and assign something from below which is not visible **Actual Result**: If I don't know the correct search term, it's impossible to make the desired role appear in the menu. **Expected Result**: I'd want to have either a scrollbar or the ability to use keyboard arrows to discover the role items in the menu. None of them is possible at the moment. **Relevant WCAG Criteria:** [#.#.# WCAG Criterion](link to https://www.w3.org/WAI/WCAG21/quickref/?versions=2.0) **Environment**: - Grafana version: 12.4.0-21125823918.patch4 (current steady RRC) - Data source type & version: - - User OS & Browser: Fedora 42, Brave 1.86.139 - Others: only mouse and keyboard (no touchpad), scroll wheel disabled on the mouse