test/twisted: export XDG_CONFIG_HOME, XDG_CONFIG_DIRS for completeness
test/twisted: export XDG_CONFIG_HOME, XDG_CONFIG_DIRS for completeness

It's another well-known directory prefix that we should divert into our
tests directory.

freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control