Refresh rates are an important information for users, even if they
can't change them.
This is especially true for cases where knowledge of the refresh
rate may influence the decission about the resolution to use.
Consider the example where a display may support `3840x2160@60Hz`
and `2560x1440@144Hz`. When choosing `3840x2160` as resolution,
the refresh rate will likely get hidden, making the user unaware
of the fact that they will maybe not get what they want (potentially
144Hz).
So follow the example of e.g. the sound panel where input and output
devices are listed in dropdowns, even if they are the only options
selectable.
Note: while this is a design change, for a big group of users this
won't actually change the default experience as Mutter until recently
had a bug to duplicate 60Hz modes in many cases. So most laptop users
already saw the refresh rate panel in previous Gnome versions,
dispite it having little use.
See also:
fb9564b87b
375bbc333c