`release-please` doesn't understand conventional rubygems pre-release versioning

#### Environment details

- OS: Linux
- Node.js version: 16.17.1
- npm version: 8.15.0
- `release-please` version: 15.9.1 / main branch on this repo

#### Steps to reproduce

1. Try and release a Ruby gem with version number 1.0.0.alpha.1 (via empty commit, manifest, or any other way)
2. release-please will create a release for v1.0.0 completely ignoring the .alpha.1 part
3. Try and release the same Ruby gem with version number 1.0.0-alpha1 (via empty commit, manifest, or any other way)
4. release-please will create a release for v1.0.0-alpha1

#### More details

Ruby uses their own twist on semver when it comes to prereleases. https://guides.rubygems.org/patterns/#prerelease-gems recommends versioning gems as `...`. Following the semver spec, it should be `..-

`. 


The current behavior of `release-please` doesn't support the recommended prerelease versioning format for Ruby gems and will release a full version instead of a prerelease.