lib: Fix wording in a g_warning()
lib: Fix wording in a g_warning()

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

Closes: #1338
Approved by: mwleeds

handsome-feng/flatpak,handsome-feng/flatpak,flatpak/flatpak,flatpak/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak