rake fails on Ubuntu 22.04

srh@pc11:~/rdbsite/docs$ rake 
cp -r _jekyll/_standalone/assets/. assets/
cp -r _jekyll/_images/. assets/images/docs/
cp -r _jekyll/_data/. _data/docs/
cp -r _jekyll/_includes/. _includes/docs/
cp -r _jekyll/_standalone/_layouts/. _layouts/
cp -r _jekyll/_standalone/_plugins/. _plugins/
bundle exec jekyll serve --trace --watch
Configuration file: /home/srh/rdbsite/docs/_config.yml
            Source: /home/srh/rdbsite/docs
       Destination: /home/srh/rdbsite/docs/_site
 Incremental build: disabled. Enable with --incremental
      Generating... 
                    done in 12.669 seconds.
 Auto-regeneration: enabled for '/home/srh/rdbsite/docs'
/var/lib/gems/3.0.0/gems/jekyll-3.9.2/lib/jekyll/commands/serve/servlet.rb:3:in `require': cannot load such file -- webrick (LoadError)
	from /var/lib/gems/3.0.0/gems/jekyll-3.9.2/lib/jekyll/commands/serve/servlet.rb:3:in `<top (required)>'
	from /var/lib/gems/3.0.0/gems/jekyll-3.9.2/lib/jekyll/commands/serve.rb:184:in `require_relative'
	from /var/lib/gems/3.0.0/gems/jekyll-3.9.2/lib/jekyll/commands/serve.rb:184:in `setup'
	from /var/lib/gems/3.0.0/gems/jekyll-3.9.2/lib/jekyll/commands/serve.rb:102:in `process'
	from /var/lib/gems/3.0.0/gems/jekyll-3.9.2/lib/jekyll/commands/serve.rb:93:in `block in start'
	from /var/lib/gems/3.0.0/gems/jekyll-3.9.2/lib/jekyll/commands/serve.rb:93:in `each'
	from /var/lib/gems/3.0.0/gems/jekyll-3.9.2/lib/jekyll/commands/serve.rb:93:in `start'
	from /var/lib/gems/3.0.0/gems/jekyll-3.9.2/lib/jekyll/commands/serve.rb:75:in `block (2 levels) in init_with_program'
	from /var/lib/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `block in execute'
	from /var/lib/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `each'
	from /var/lib/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `execute'
	from /var/lib/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary/program.rb:42:in `go'
	from /var/lib/gems/3.0.0/gems/mercenary-0.3.6/lib/mercenary.rb:19:in `program'
	from /var/lib/gems/3.0.0/gems/jekyll-3.9.2/exe/jekyll:15:in `<top (required)>'
	from /usr/local/bin/jekyll:25:in `load'
	from /usr/local/bin/jekyll:25:in `<main>'
rake aborted!
Command failed with status (1): [bundle exec jekyll serve --trace --watch...]
/home/srh/rdbsite/docs/Rakefile:98:in `jekyll'
/home/srh/rdbsite/docs/Rakefile:86:in `block in <top (required)>'
/usr/share/rubygems-integration/all/gems/rake-13.0.6/exe/rake:27:in `<top (required)>'
Tasks: TOP => default => serve
(See full trace by running task with --trace)

Reproduce the failure on Ubuntu 22.04 by running rake in the docs directory. Start at Rakefile:98 and the bundle exec jekyll serve --trace --watch entry point, then investigate the reported missing webrick dependency. Done means the default rake task starts Jekyll without the LoadError.