common: Mark an error message as translatable
common: Mark an error message as translatable

All the other error messages in that file are.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #2609
Approved by: matthiasclasen

matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak