d/librem5-ci.yml: simplify CI

Fixes #1
6 jobs for byz_simplify_ci in 6 minutes and 9 seconds
Status Job ID Name Coverage
  Package
passed #328926
librem5
package-pureos-byzantium

00:02:02

passed #328922
librem5:arm64
package-pureos-byzantium:arm64

00:06:09

failed #328921
librem5
package-pureos-byzantium

00:00:18

 
  Test Package
passed #328923
librem5
autopkgtest-pureos-byzantium-package

00:01:17

passed #328925
librem5
check-tarball

00:00:51

passed #328924
librem5
lintian-pureos-byzantium-package

00:00:31