docs(list): fix single selection example selection display (#19731)

The single selection example was previously rendering `[object Object]` instead of the selected value

Author: swseverance

src/components-examples/material/list/list-single-selection/list-single-selection-example.html

@@ -1,9 +1,9 @@
 <mat-selection-list #shoes [multiple]="false">
-  <mat-list-option *ngFor="let shoe of typesOfShoes">
+  <mat-list-option *ngFor="let shoe of typesOfShoes" [value]="shoe">
     {{shoe}}
   </mat-list-option>
 </mat-selection-list>
 
 <p>
-  Option selected: {{shoes.selectedOptions.selected}}
+  Option selected: {{shoes.selectedOptions.selected[0]?.value}}
 </p>