Build/Test Tools: Reclassify `json2php` as a `devDependency`.

This dependency is responsible for transforming some JSON files to PHP ones. But since this is not included in the distributed software, it should not be specified as a `dependency`.

Props nimeshatxecurify, royhridoy, phpbits, dilip2615, noruzzaman.
Fixes #64221.

git-svn-id: https://develop.svn.wordpress.org/trunk@62061 602fd350-edb4-49c9-b593-d223f7449a82