Can't install prerelease RubyGems #945

Ensure the following before filing this issue

• I verified it reproduces with the latest version with - uses: ruby/setup-ruby@v1 (see Versioning policy)

• I tried to reproduce the issue locally by following the workflow steps (including all commands done by ruby/setup-ruby, except for Downloading Ruby & Extracting Ruby),
  and it did not reproduce locally (if it does reproduce locally, it's not a ruby/setup-ruby issue)

Are you running on a GitHub-hosted runner or a self-hosted runner?

GitHub-hosted runner

Link to the failed workflow job (must be a public workflow job, so the necessary information is available)

http://github.com/haines/pg-aws_rds_iam/actions/runs/37953659583/job/113898580616#step:3:54

Any other notes?

The prerelease version format for RubyGems (e.g. 4.1.0.beta2) is not valid semantic versioning, so the semver module (correctly) reports that it is invalid. The comparison needs to take this into account in order for this action to be able to install such a version.