Update colour contrast formula with new constant from WCAG 2.2 (#37731)

See https://github.com/w3c/wcag/pull/1780

Closes #37022

scss/_functions.scss

@@ -188,7 +188,7 @@ $_luminance-list: .0008 .001 .0011 .0013 .0015 .0017 .002 .0022 .0025 .0027 .003
   );
 
   @each $name, $value in $rgb {
-    $value: if(divide($value, 255) < .03928, divide(divide($value, 255), 12.92), nth($_luminance-list, $value + 1));
+    $value: if(divide($value, 255) < .04045, divide(divide($value, 255), 12.92), nth($_luminance-list, $value + 1));
     $rgb: map-merge($rgb, ($name: $value));
   }