media-sound/lollypop: add USE dep default for g-introspection[cairo]

media-sound/lollypop: add USE dep default for g-introspection[cairo]

The cairo USE flag was a bit bogus on gobject-introspection, so with the
meson port it got removed, as it really only controlled some tests for
upstream. The cairo bindings are always installed, and presumably any
consumer needing them will have a dep on cairo directly or indirectly
already anyhow - at least lollypop does via pycairo.

Package-Manager: Portage-2.3.84, Repoman-2.3.20
Signed-off-by: Mart Raudsepp <leio@gentoo.org>