Fix UI focus being shown when it shouldn't

[YeldhamDev]

This can be reproduced by toggling plugins in the settings dialog, as it will show the focus outline when doing so.

[KoBeWi]

Now the focus does not appear with keyboard:

godot.windows.editor.dev.x86_64_lQN0MFAGkE.mp4

EDIT:
Ah, you need to Tab from another control. Navigating the unfocused list does not focus it. Is it intended?

[YeldhamDev]

@KoBeWi Sorry for the late response, but yeah, it's intentional. The highlighting already does the job well, and it looks odd to bluntly switch to the focus style by just using the arrow keys while already inside of it.

[Repiteo]

Thanks!