gui2/button: Fix highlight colour for the disabled state

It was apparently copy-pasted from the pressed state. This resulted in
disabled buttons looking like they are pressed.

[ci skip]

changelog.md

@@ -535,6 +535,7 @@
  ### User interface
    * Do not list nameless abilities in the Abilities and Ability Upgrades lists in unit
      descriptions in Help (issue #3060).
+   * Fixed disabled buttons using the pressed highlight color.
  ### Miscellaneous and bug fixes
    * Made wmllint recognize [remove_time_area] in order to avoid spurious warnings about
      unit ids.

data/gui/widget/button_default.cfg

@@ -111,7 +111,7 @@
 				{_GUI_STATE "background"
 					({GUI__FONT_COLOR_DISABLED__DEFAULT ALPHA={ALPHA}})
 					("89,  89,  89,  {ALPHA}")
-					("1, 10, 16, 255") "~GS(){IPF}"}
+					("60,  60,  60, 255") "~GS(){IPF}"}
 
 				{GUI__CENTERED_TEXT ({FONT_SIZE}) () ({GUI__FONT_COLOR_DISABLED__TITLE})}