style(experience): change logto logo color (#7914)

Author: wangsijie

packages/experience/src/components/LogtoSignature/index.module.scss

@@ -5,7 +5,7 @@
   @include _.flex-row;
   font: var(--font-label-2);
   font-weight: normal;
-  color: var(--color-neutral-variant-70);
+  color: var(--color-neutral-variant-60);
   padding: _.unit(1) _.unit(2);
   text-decoration: none;
   opacity: 75%;