macosx: Include NSAppearanceNameVibrantDark in dark mode detection, fixing borked labels

In master, some labels are coloured incorrectly due to a faulty check for dark mode which doesn't account for NSAppearanceNameVibrantDark. This PR adds this appearance to the dark mode check.

Fixed:

Prior to fix:

Signed-off-by: Claudio Cambra claudio.cambra@gmail.com