amber/byzantium-jobs: Update the arm64 image name

`pureos/amber` and `pureos/byzantium` images now have a manifest
that allows the right image to be selected based on host architecture
automatically.
4 jobs for arm in 2 minutes and 1 second (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #332382
librem5
test:native

00:00:11

 
  Package
passed #332383
librem5
package-debian-buster

00:01:02

 
  Test Package
passed #332384
librem5
autopkgtest-debian-buster-package

00:00:40

passed #332385
librem5
lintian-debian-buster-package

00:00:44