lockscreen: Fix multiline action button alignment

Action button labels can wrap to multiple lines depending on the translation, which shifts vertically centered buttons.

Align the lock screen action buttons to the top so their icons stay on the same horizontal line regardless of label height.

Another option would be to give labels more horizontal space to reduce wrapping. However, varying button widths would make spacing inconsistent unless a common width is calculated from the widest label. Increasing the spacing slightly may still help some translations, but the alignment fix is more general.