CI: change arm runner tag

2 jobs for flatpak_arm in 5 minutes and 36 seconds (queued for 1 minute and 41 seconds)
latest
Status Job ID Name Coverage
  Build Flatpak
failed #237491
flatpak
flatpak:master

00:05:36

 
  Build Arm Flatpak
skipped #237492
librem5:arm64:priv
flatpak-arm64:master
 
Name Stage Failure
failed
flatpak:master Build Flatpak
Export failed: Child process exited with code 1
Uploading artifacts...
WARNING: contacts-dev.flatpak: no matching files
_build/meson-logs/: found 5 matching files

Uploading artifacts to coordinator... ok
id=237491 responseStatus=201 Created token=hTKNRC6b
Uploading artifacts...
WARNING: _build/flatpak:master-report.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1