postmarketos-ui-(lxqt|mate): depend on DejaVu

MR 5540 breaks the Enter key label in onboard OSK with LXQt and Mate. In
theory Droid can be used instead, but it actually does not work.

We can't use _pmb_recommends here since v24.06 -> v24.12 upgrade will
break onboard unless any package depends on font-dejavu.

Signed-off-by: Masanori Ogino <mogino@acm.org>
[ci:skip-build]: already built successfully in CI