docs: add missing syntax highlight (#21722)
docs: add missing syntax highlight (#21722)

* docs: add missing syntax highlight

* docs: add title to json example

* Apply suggestions from code review

Co-Authored-By: LB <8468275f0d120527324004754c3d088324306866@gatsbyjs.com>

Co-authored-by: LB <8468275f0d120527324004754c3d088324306866@gatsbyjs.com>

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