docs(toolbar): add aria-labels to icons in example (#15128)

Fixes #15041

Author: Suresh918

src/material-examples/toolbar-multirow/toolbar-multirow-example.html

@@ -6,13 +6,13 @@
   <mat-toolbar-row>
     <span>Second Line</span>
     <span class="example-spacer"></span>
-    <mat-icon class="example-icon">verified_user</mat-icon>
+    <mat-icon class="example-icon" aria-hidden="false" aria-label="Example user verified icon">verified_user</mat-icon>
   </mat-toolbar-row>
 
   <mat-toolbar-row>
     <span>Third Line</span>
     <span class="example-spacer"></span>
-    <mat-icon class="example-icon">favorite</mat-icon>
-    <mat-icon class="example-icon">delete</mat-icon>
+    <mat-icon class="example-icon" aria-hidden="false" aria-label="Example heart icon">favorite</mat-icon>
+    <mat-icon class="example-icon" aria-hidden="false" aria-label="Example delete icon">delete</mat-icon>
   </mat-toolbar-row>
 </mat-toolbar>