Creating a Ruby 2 variant for testing

[BretFisher]

Making a Ruby 2 variant of this image for easier testing. No plans to accept this PR unless it turns out Ruby 3 is still bad for Jekyll. Hoping this will help with #82

[BretFisher]

Hmm, builds fail, investigating.

[github-actions]

Docker image tag(s) pushed:

bretfisher/jekyll:pr-84
bretfisher/jekyll:gha-3963823201
ghcr.io/bretfisher/jekyll:pr-84
ghcr.io/bretfisher/jekyll:gha-3963823201 

Labels added to images:

org.opencontainers.image.title=jekyll-serve
org.opencontainers.image.description=Jekyll in a Docker Container For Easy SSG Development
org.opencontainers.image.url=https://github.com/BretFisher/jekyll-serve
org.opencontainers.image.source=https://github.com/BretFisher/jekyll-serve
org.opencontainers.image.version=pr-84
org.opencontainers.image.created=2023-01-20T01:12:26.265Z
org.opencontainers.image.revision=6387c031c9a692925a7b447c488a2169122bd12f
org.opencontainers.image.licenses=MIT