Summary

Closes #6795

The noUnassignedVariables rule was incorrectly flagging variables used in JSX ref attributes as
unassigned. This occurred because JSX ref attributes were not being recognized as write references in the
semantic analyzer.

This PR fixes the issue by adding proper detection for JSX ref attribute usage, ensuring that variables
assigned to ref props are correctly tracked as write references.

Test Plan

Added test cases in crates/biome_js_analyze/tests/specs/nursery/noUnassignedVariables/valid.jsx to verify
that JSX ref attributes are correctly handled:

export const Bug = () => {
    let value;
    return <div ref={value} />
}

The snapshot test confirms that no diagnostic is generated for this valid usage pattern.

Docs

no-unassigned-variables