Disable html_safe check for JSON.pretty_generate

[hlascelles]

We are seeing "erb interpolation with '<%= (...).html_safe %>' in this context is never safe" errors for this:

<%= JSON.pretty_generate(foo: :bar).html_safe %>

Due to this: https://github.com/Shopify/better-html/blob/121065400314db191cae7202073cdc8b9125b4bb/lib/better_html/test_helper/safe_erb/tag_interpolation.rb#L175

Should we make JSON.pretty_generate be "safeable" by default?