Fix difficulty slider focus handling in song select

[ryawaa]

i feel like theres a better way to do this, if you think so, please let me know.

fixes #31559

[bdach]

There definitely is a much better way to do this, and a one-liner sketch of such a way follows:

diff --git a/osu.Game/Graphics/UserInterface/RangeSlider.cs b/osu.Game/Graphics/UserInterface/RangeSlider.cs
index 422c2ca4a3..5638c217c9 100644
--- a/osu.Game/Graphics/UserInterface/RangeSlider.cs
+++ b/osu.Game/Graphics/UserInterface/RangeSlider.cs
@@ -164,6 +164,8 @@ protected partial class BoundSlider : RoundedSliderBar<double>
         {
             public new Nub Nub => base.Nub;
 
+            public override bool AcceptsFocus => false;
+
             public string? DefaultString;
             public LocalisableString? DefaultTooltip;
             public string? TooltipSuffix;

You could say that this override should be constrained only to the specific usage site of the range slider in song select; figuring out how to achieve that is left as an exercise to the reader.