Fix focus glow appearing above range slider's nubs

osu.Game/Graphics/UserInterface/RangeSlider.cs

@@ -115,7 +115,9 @@ public RangeSlider()
                     KeyboardStep = 0.1f,
                     RelativeSizeAxes = Axes.X,
                     Y = vertical_offset,
-                }
+                },
+                upperBound.Nub.CreateProxy(),
+                lowerBound.Nub.CreateProxy(),
             };
         }
 
@@ -160,6 +162,8 @@ public override bool ReceivePositionalInputAt(Vector2 screenSpacePos) =>
 
         protected partial class BoundSlider : RoundedSliderBar<double>
         {
+            public new Nub Nub => base.Nub;
+
             public string? DefaultString;
             public LocalisableString? DefaultTooltip;
             public string? TooltipSuffix;