Fix group vertical spacing

Author: vanifatovvlad

Editor/Elements/TriHeaderGroupBaseElement.cs

@@ -52,6 +52,8 @@ public sealed override void OnGUI(Rect position)
             {
                 xMin = contentBgRect.xMin + InsetLeft,
                 xMax = contentBgRect.xMax - InsetRight,
+                yMin = contentBgRect.yMin + InsetTop,
+                yMax = contentBgRect.yMax - InsetBottom,
                 height = contentHeight,
             };