docs: fix shadow variable in tutorial example

[Hearen]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.io application / infrastructure changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

[IgorMinar]

Can you please explain the motivation for this change?

It would have been easier for us to review this change ifbthe motivation was captured in the commit message body.

[Hearen]

@IgorMinar This is a tiny issue I found when following the tutorial, my VSCode just warn me of this hero will be shadowed by the parameter who has the same name as hero while actually the hero object should be a new hero returned from backend.

[IgorMinar]

Ah! That makes sense. Thank you! Please include this kind of explanation in future PRs. Thanks again.

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