Dropdown/Listbox warning text if button is disabled while loading

The "GlDisclosureDropdown/GlCollapsibleListbox: Toggle is missing a 'tabindex' and cannot be focused" warning is triggered by dropdowns that are disabled while loading.

e.g.

<gl-collapsible-listbox
  :toggle-text="Pick something"
  :disabled="loading"
/>

Maybe just means we shouldn't be disabling buttons