Update _custom-forms.scss (#40350)

Author: dgrammatiko

build/media_source/templates/administrator/atum/scss/vendor/bootstrap/_custom-forms.scss

@@ -52,6 +52,8 @@
 
   &:disabled {
     cursor: default;
+    background-color: #e8e8e8;
+    background-image: none;
     border: 0;
     box-shadow: none;
   }