Pin github-pages nokogiri version…

[tianon]

… (using "twiddle-wakka"/"~>" so we get 1.15.5 instead of 1.15.4)

This works around our recent build failures.

Ultimately, it seems I'll have to just stop maintaining this image at some point (github/pages-gem#752 (comment)) 😞

(Everything I can find seems to suggest that users who care should start using Jekyll directly via GHA instead of relying on github-pages 😞)

[tianon]

ERROR:  Error installing github-pages:
	The last version of faraday-net_http (>= 2.0, < 3.2) to support your Ruby & RubyGems was 3.0.2. Try installing it with `gem install faraday-net_http -v 3.0.2` and then running the current command again
	faraday-net_http requires Ruby version >= 3.0.0. The current ruby version is 2.7.8.225.

I'm going to eat a shoe.

[tianon]

😭 faraday-net_http is not even a module listed in https://pages.github.com/versions.json

[tianon]

Yeah, that's plenty - I'm done. Sorry GitHub Pages, but I'm way over it.

[tianon]

8cdc410