bug#57292: GDM accessibility menu buttons don't do anything

[Maxim Cournoyer]

Hello Guix!

I've just noticed that the accessibility buttons at the top right of the
screen, e.g. "High Contrast" don't stick in the enable position, and do
seem to do anything.  Both in 40.1 and the 42.0 I'm about to update to.

Thanks,

Maxim