CI: use ARM64 to build flatpak

2 jobs for arm-flatpak in 11 minutes and 26 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build Flatpak
passed #201380
flatpak
flatpak:master

00:05:07

 
  Build Arm Flatpak
passed #201381
ARM64
flatpak-arm64:master

00:06:18