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-docs/commit-message-guidelines.md
• Tests for the changes have been added (not applicable)
• Docs have been added / updated

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.dev application / infrastructure changes
• Other... Please describe:

What is the current behavior?

The whitespace guide contains a malformed HTML comment:

<!-- prettier-ignore>

Issue Number: N/A

What is the new behavior?

Updates the malformed comment to valid HTML comment syntax:

<!-- prettier-ignore -->

This makes the comment syntax valid and consistent with the other prettier-ignore comment in the same document.

Does this PR introduce a breaking change?

• Yes
• No

Other information

This is a documentation-only change and does not affect application behavior.