Tree: Increase css weight (#16799)

packages/theme-chalk/src/cascader-panel.scss

@@ -110,10 +110,6 @@
     text-overflow: ellipsis;
   }
 
-  > .el-checkbox {
-    margin-right: 0;
-  }
-
   > .el-radio {
     margin-right: 0;
 

packages/theme-chalk/src/tree.scss

@@ -59,7 +59,7 @@
     & > .el-tree-node__expand-icon {
       padding: 6px;
     }
-    & > .el-checkbox {
+    & > label.el-checkbox {
       margin-right: 8px;
     }
     &:hover {