fix: steps nav active line height, 3px -> 2px (#24829)

Co-authored-by: 愚道 <tingzhao.ytz@antfin.com>

components/steps/style/nav.less

@@ -76,7 +76,7 @@
       left: 50%;
       display: inline-block;
       width: 0;
-      height: 3px;
+      height: 2px;
       background-color: @steps-nav-active-color;
       transition: width 0.3s, left 0.3s;
       transition-timing-function: ease-out;