Fixup: address JSON loading as fixed UTF-8 encoding

What does this MR do?

Fixup: address JSON loading as fixed UTF-8 encoding

Replace JSON.parse(File.read()) with JSON.load_file() post JSON 2.8.2+ This ensures File.read(path, :encoding => Encoding::UTF_8) as see in https://github.com/ruby/json/commit/3a8505a8fa39711a957b2fc942862a874a8e8bef

JSON interchange specifically rfc8259, section 8.1 indicates that we should always expect these files to be UTF8

https://datatracker.ietf.org/doc/html/rfc8259#section-8.1

• Should be backported to 17.10, which includes JSON 2.10.1
• Not needed before 17.10, as JSON <= 2.7.x

Closes #8995 (closed)

Changelog: fixed

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Closes #8995 (closed)