Add explicit irb dependency

Under Ruby 3.4, `bake utopia:shell` logs the warning

```
/<snip>/utopia-2.30.0/lib/utopia/shell.rb:8: warning: irb was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add irb to your Gemfile or gemspec to silence this warning.
```

Add an explicit dependency on the `irb` gem to the gemspec.

Author: mjq

utopia.gemspec

@@ -28,6 +28,7 @@ Gem::Specification.new do |spec|
 	spec.add_dependency "concurrent-ruby", "~> 1.2"
 	spec.add_dependency "console", "~> 1.24"
 	spec.add_dependency "http-accept", "~> 2.1"
+	spec.add_dependency "irb"
 	spec.add_dependency "mail", "~> 2.6"
 	spec.add_dependency "mime-types", "~> 3.0"
 	spec.add_dependency "msgpack"