Fix jekyll serve failing with Ruby 3.0

bundle exec jekyll serve --future

fails with

/vendor/bundle/ruby/3.0.0/gems/jekyll-4.2.0/lib/jekyll/commands/serve/servlet.rb:3:in `require': cannot load such file -- webrick (LoadError)

Compare with https://github.com/jekyll/jekyll/issues/8523

added Bug Progress::4_Can review labels

requested review from @jandt-desy

assigned to @frust45

changed title from Fix jekyll serve failing with Jekyll 3.0 to Fix jekyll serve failing with Ruby 3.0

approved this merge request

merged

mentioned in commit f2dbcd57