The example already uses the signal-based input() but still declares items with the @ContentChildren decorator. Convert to the signal-based contentChildren() query for consistency.

PR Checklist

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

What is the current behavior?

The MyMenu example in the component harness guide uses the signal-based input() but declares its content query with the decorator-based @ContentChildren, mixing the two styles in the same example

Issue Number: N/A

What is the new behavior?

The query now uses the signal-based contentChildren() function (items = contentChildren(MyMenuItem)), matching the modern style of the surrounding input() call.

Does this PR introduce a breaking change?

• Yes
• No