gitlab-ci: Build debs

Override upstream CI to build Debian packages
4 jobs for hidpi-avatars in 7 minutes and 5 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Package
passed #273419
librem5
package:deb-debian-buster

00:02:06

passed #273420
librem5:arm64
package:deb-debian-buster:arm64

00:05:36

 
  Test Package
passed #273421
librem5
autopkgtest-debian-buster-package

00:00:57

passed #273422
librem5
lintian-debian-buster-package

00:00:54