fix(tree): fix typo in CSS class name (#17538)

Author: MaximBalaganskiy

src/material/tree/tree.scss

@@ -13,6 +13,6 @@ $mat-node-height: 48px;
   word-wrap: break-word;
 }
 
-.mat-nested-tree-ndoe {
+.mat-nested-tree-node {
   border-bottom-width: 0;
 }