Inject site.github via :pre_render step rather than :after_init

[parkr]

Jekyll 4 has a call to site.config.inspect, which renders all the values in site.config['github'].
This causes all of the API calls to be resolved regardless of whether the user is using them.
This patch should allow Jekyll 4 to call site.config.inspect without causing the large number of API calls.

Fixes #237.

[ashmaroli]

Thank you for tackling the linked issue this quickly, @parkr.
Hope you don't mind waiting a couple of days for my review.

After a cursory pass-through, I would like to leave some suggestions,though:

• For better readability, it'd be better if the hooks were contained under the plugin's namespace. Additionally, inject_payload! sounds wrong to me. We're technically injecting GH metadata into the payload So, how about inject_metadata! (or perhaps munge_payload! instead)?:

  module Jekyll
    module GitHubMetadata
      class SiteGitHubMunger
        # ...
  
        def inject_metadata!(payload)
          payload.site["github"] = github_namespace
        end
        alias_method :munge_payload!, :inject_metadata! # for illustration purpose only
  
        # ...
      end
  
      Jekyll::Hooks.register :site, :after_init do |site|
        SiteGitHubMunger.global_munger = SiteGitHubMunger.new(site)
        SiteGitHubMunger.global_munger.munge!
      end
  
      Jekyll::Hooks.register :site, :pre_render do |_site, payload|
        SiteGitHubMunger.global_munger.inject_metadata!(payload)
      end
  
    end # end GitHubMetadata
  end

• The changes to Gemfile and script/test-site do not seem to have significance to this PR. Perhaps, you could commit them directly to main instead?
• While you're updating the main branch, I think AppVeyor should stop testing with Ruby 2.4.

[parkr]

@ashmaroli Updated! Your review was quick – only 9 hours by my count!

[ashmaroli]

LGTM expect for two instances of nitpicking.
Either ways, feel free to address the comments / merge at your discretion.

[ashmaroli]

Now that payload is munged outside the #munge! method, perhaps we can assign the metadata directly..

payload.site["github"] = case site.config["github"]
                           ...
                         end

Not a blocker to merge current PR, though.

[parkr]

@jekyllbot: merge +bug