Update setup/ruby used in gh-pages workflow because it is failing on ci

[tompng]

Deploy IRB documentation to GitHub Pages is failing from about two weeks ago.

https://github.com/ruby/irb/actions/runs/11311482138

Run ruby/setup-ruby@1198b074305f9356bd56dd4b311757cc0dab2f1c
  with:
    ruby-version: 3.3
    bundler-cache: true
Error: The current runner (ubuntu-[2](https://github.com/ruby/irb/actions/runs/11311482138/job/31457768381#step:3:2)4.04-x64) was detected as self-hosted because the platform does not match a GitHub-hosted runner image (or that image is deprecated and no longer supported).

Updated to latest. I'm not sure this fixes the failure it or not.

[st0012]

Thank you! Let's see how it goes.
BTW, after ruby/rdoc#1191 is merged I'd also like to use it in IRB by pointing to the latest rdoc until it's released.