os-database: Only show supported architectures in "Download an OS"

Fixes #387
5 jobs for filter-off-unsupported-arches in 54 minutes and 11 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #391692
flatpak

00:40:55

failed #391656
flatpak

00:32:12

 
  Review
passed #391657
review

00:06:07

manual #391658
allowed to fail manual
stop_review
 
  Cross Distro
passed #391659
fedora:rawhide

00:07:07