fix(Steps): fix the style that occurs when there is only one step (#11822)

packages/vant/src/step/index.less

@@ -42,7 +42,7 @@
       }
     }
 
-    &:last-child {
+    &:last-child:not(:first-child) {
       position: absolute;
       right: 1px;
       width: auto;