image_test/ruby: instal a web server

It should fix this error:
+ ruby /src/ruby.rb
/usr/local/bundle/gems/rackup-2.2.0/lib/rackup/handler.rb:81:in `pick': Couldn't find handler for: puma, falcon, thin, HTTP, webrick. (LoadError)
	from /usr/local/bundle/gems/sinatra-4.0.0/lib/sinatra/base.rb:1624:in `run!'
	from /usr/local/bundle/gems/sinatra-4.0.0/lib/sinatra/main.rb:47:in `block in <module:Sinatra>'

PiperOrigin-RevId: 693089452

images/basic/ruby/Dockerfile

@@ -1 +1 @@
-FROM ruby:3.2.3
+FROM ruby:3.3.5

test/image/ruby.sh

@@ -16,5 +16,5 @@
 
 set -e
 
-gem install sinatra rackup
+gem install sinatra rackup puma
 ruby /src/ruby.rb