build(deps-dev): bump @eslint/markdown from 6.3.0 to 6.4.0 (#3541)

Bumps [@eslint/markdown](https://github.com/eslint/markdown) from 6.3.0 to 6.4.0.
- [Release notes](https://github.com/eslint/markdown/releases)
- [Changelog](https://github.com/eslint/markdown/blob/main/CHANGELOG.md)
- [Commits](eslint/markdown@v6.3.0...v6.4.0)

---
updated-dependencies:
- dependency-name: "@eslint/markdown"
  dependency-version: 6.4.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]