Error: input ruby-version needs to be specified if no .ruby-version or .tool-versions file exists can be confusing

[dblock]

Error: input ruby-version needs to be specified if no .ruby-version or .tool-versions file exists

https://github.com/dblock/ruby-enum/actions/runs/20601440553/job/59167763793

Run ruby/setup-ruby@v1
Error: Error: input ruby-version needs to be specified if no .ruby-version or .tool-versions file exists
    at parseRubyEngineAndVersion (/home/runner/work/_actions/ruby/setup-ruby/v1/dist/index.js:85398:13)
    at setupRuby (/home/runner/work/_actions/ruby/setup-ruby/v1/dist/index.js:85334:35)
    at run (/home/runner/work/_actions/ruby/setup-ruby/v1/dist/index.js:85308:11)
    at /home/runner/work/_actions/ruby/setup-ruby/v1/dist/index.js:85509:40
    at /home/runner/work/_actions/ruby/setup-ruby/v1/dist/index.js:85511:3
    at Object.<anonymous> (/home/runner/work/_actions/ruby/setup-ruby/v1/dist/index.js:85514:12)
    at Module._compile (node:internal/modules/cjs/loader:1521:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1623:10)
    at Module.load (node:internal/modules/cjs/loader:1266:32)
    at Module._load (node:internal/modules/cjs/loader:1091:12)

Took me a while to understand that I needed to specify the ruby version as input, will add to README.

[dblock]

I defaulted the Ruby version in #4, I think that's easier.