fix(docs-infra): fix menu icon size (#52689)

Fixes that the hamburger icon was too small, because the top nav is using the wrong kind of button. Switching it to the right one would require more refactoring so I went with the simpler approach for now.

PR Close #52689

aio/src/styles/1-layouts/top-menu/_top-menu.scss

@@ -66,8 +66,13 @@ mat-toolbar.app-toolbar {
       transition-timing-function: cubic-bezier(0.25, 0.8, 0.25, 1);
     }
 
+    // TODO: this override is necessary, because the menu is using
+    // the wrong kind of button (text button instead of icon button).
     & .mat-icon {
       position: inherit;
+      width: 24px;
+      height: 24px;
+      margin: 0;
     }
   }