AvatarSelector: fix hidpi, avatars are to small

Fix https://source.puri.sm/Librem5/gnome-contacts/issues/37
3 jobs for avatar_scaling in 5 minutes and 20 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Build Flatpak
failed #237285
flatpak
flatpak:master

00:05:20

failed #237283
flatpak
flatpak:master

00:05:33

 
  Build Arm Flatpak
skipped #237284
ARM64
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=237285 responseStatus=201 Created token=ovXTikCr
Uploading artifacts...
WARNING: _build/flatpak:master-report.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1