Merge pull request #17228 from ant-design/fix-sider-z-index

fix: Layout sider trigger z-index too low

components/layout/style/index.less

@@ -96,6 +96,7 @@
         position: absolute;
         top: @layout-header-height;
         right: -@layout-zero-trigger-width;
+        z-index: 1;
         width: @layout-zero-trigger-width;
         height: @layout-zero-trigger-height;
         color: @layout-trigger-color;