Mark postinst-prerm and postinst-prerm-core as xfail
https://lava.collabora.co.uk/results/1789334/3_canterbury
Signed-off-by: Frédéric Dalleau frederic.dalleau@collabora.com
https://lava.collabora.co.uk/results/1789334/3_canterbury
Signed-off-by: Frédéric Dalleau frederic.dalleau@collabora.com