CI: use arm image

3 jobs for backport in 55 minutes and 22 seconds (queued for 2 minutes and 40 seconds)
latest
Status Job ID Name Coverage
  .Pre
passed #237684
flatpak
flatpak

00:07:18

passed #237501
librem5:arm64:priv
flatpak-arm64

00:48:03

failed #237500
flatpak
flatpak

00:05:33