docs: change count to this.count in example

[bahalbach]

count is not available in this context, the instance variable this.count should be used instead.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/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?

In the example count is not available in this context, the instance variable this.count should be used instead.

Issue Number: N/A

What is the new behavior?

The example does not have an error.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[JeanMeche]

LGTM

[pkozlowski-opensource]

This PR was merged into the repository by commit df267c5.