fix(frontmatter): prevent slug duplication through frontmatter (#1860)
* fix(frontmatter): prevent slug duplication through frontmatter
* Simplify duplicate slug checks
* Update quartz/plugins/transformers/frontmatter.ts
Co-authored-by: Jacky Zhao <j.zhao2k19@gmail.com>
* lint
---------
Co-authored-by: Jacky Zhao <j.zhao2k19@gmail.com>
authored by