GlDropdown is inaccessible after secondary open

If you open GlDropdown twice it will become inaccessible for a screen reader like VoiceOver.

To reproduce:

1. Configure VoiceOver to use 'Grouping items' mode for web browsing

   

2. Start VoiceOver

3. Select any dropdown button toggle

4. Perform default action (VO-Space bar)

5. Navigate into dropdown content (VO-Shift-Down Arrow)

6. Navigate back to dropdown toggle

7. Activate toggle

8. Activate toggle again to show dropdown content

9. Navigate into dropdown content

10. Observe that it's not possible anymore

Screen_Recording_2025-04-29_at_03.56.27