fix(steps): fix the spacing error between title and description (#3898)

Author: anlyyao

packages/components/step-item/step-item.less

@@ -79,6 +79,10 @@
     align-items: center;
   }
 
+  &--vertical {
+    margin-bottom: 16rpx;
+  }
+
   &__anchor {
     display: flex;
     align-items: center;
@@ -150,10 +154,13 @@
       display: flex;
       align-items: center;
       justify-content: space-between;
-      margin-bottom: 8rpx;
     }
   }
 
+  &__title + &__description:not(:empty) {
+    margin-top: 8rpx;
+  }
+
   &__description {
     color: @step-item-description-color;
     line-height: 40rpx;