CI failing due to dependency issues

[elichad]

"Website build" job is now failing:

Run gem install github-pages bundler kramdown kramdown-parser-gfm
ERROR:  Error installing github-pages:
	The last version of nokogiri (>= 1.13.6, < 2.0) to support your Ruby & RubyGems was 1.15.6. Try installing it with `gem install nokogiri -v 1.15.6` and then running the current command again
	nokogiri requires Ruby version >= 3.0, < 3.4.dev. The current ruby version is 2.7.8.225.
ERROR:  Error installing bundler:
	The last version of bundler (>= 0) to support your Ruby & RubyGems was 2.4.22. Try installing it with `gem install bundler -v 2.4.22`
	bundler requires Ruby version >= 3.0.0. The current ruby version is 2.7.8.225.
Successfully installed unicode-display_width-1.8.0
Successfully installed terminal-table-1.8.0
Successfully installed kramdown-2.4.0
Successfully installed kramdown-parser-gfm-1.1.0
2 gems installed

The install and make lesson-check-all work on my machine with Ruby 3.3 (CI uses 2.7), so changing that might work - though the long-term solution is to upgrade to use the Workbench, I think.