docs(docs-infra): fix (+) not accepting null error by using `Number` instead (#41570)

Fix unexpected error when following the tutorial (when going through it with stricter type checking enforced). While (+) converts a string to an integer, it does not account for the possibility that `this.route.snapshot.paramMap.get('id')` could return null (type: string | null). Since this null case is not a practical outcome, it is a matter of types; switching from (+) to the `Number` function eliminates this issue, making the tutorial more robust.
PR Close #41570

aio/content/examples/toh-pt5/src/app/hero-detail/hero-detail.component.ts

@@ -33,7 +33,7 @@ export class HeroDetailComponent implements OnInit {
   }
 
   getHero(): void {
-    const id = +this.route.snapshot.paramMap.get('id');
+    const id = Number(this.route.snapshot.paramMap.get('id'));
     this.heroService.getHero(id)
       .subscribe(hero => this.hero = hero);
   }