bug#68213: 30.0.50; completion-preview-tests failure in --without-x build

[Eli Zaretskii]

> From: Eshel Yaron <me@eshelyaron.com>
> Cc: john muhl <jm@pub.pink>,  68213@debbugs.gnu.org
> Date: Tue, 02 Jan 2024 18:20:20 +0100
> 
> > Thanks, please try again, I hope I fixed this.
> 
> FWIW, I was going to suggest the attached patch, following how
> flymake.el handles this.  But if the current solution works, that seems
> just as good.

I don't think loading mwheel in a build --without-x is TRT.  If it
were, we'd probably preload mwheel on such a build as well.

In general, it is not safe to load packages that assume GUI
capabilities in a build that excludes those capabilities.