OBS: build_srcpkg.Dockerfile: add dh-runit
Add dh-runit, so we can build source packages of newer versions of
pcsc-lite.
Related: https://salsa.debian.org/debian/pcsc-lite/-/commit/c7c40df72dc3c754341501e34aa096fd72a61cef
Change-Id: I8d852cebb9decb3c881fd3ff9b530213bade0216
