docs: use the right tag in the HeroesComponent's template snippet (#41473)

Based on the tutorial content of the Hero Editor, the tag to be used in
HeroesComponent's template snippet should be h2 and not h3.

PR Close #41473

aio/content/examples/toh-pt1/src/app/heroes/heroes.component.1.html

@@ -3,7 +3,7 @@
 <!-- #enddocregion show-hero-1 -->
 
 <!-- #docregion show-hero-2 -->
-<h3>{{hero.name}} Details</h3>
+<h2>{{hero.name}} Details</h2>
 <div><span>id: </span>{{hero.id}}</div>
 <div><span>name: </span>{{hero.name}}</div>
 <!-- #enddocregion show-hero-2 -->