Virtual-environments: Update Ruby to 2.7

[mislav]

Tool information

• Tool name: Ruby
• Add or update? update
• Desired version: 2.7.0
• Approximate size: 30 MB (without docs)

Area for Triage: Ruby

Question, Bug, or Feature?: feature

Virtual environments affected

• [ ] macOS 10.15
• [x] Ubuntu 16.04 LTS
• [x] Ubuntu 18.04 LTS
• [ ] Windows Server 2016 R2
• [ ] Windows Server 2019

Can this tool be installed during the build?
no

Are you willing to submit a PR?
I would, but from the current installer script it's not clear to me how individual Ruby versions are installed. It looks like pre-built Ruby versions are downloaded from something called "tool cache", but the end process is opaque and I can't find how to add new Ruby versions there.

https://www.ruby-lang.org/en/news/2019/12/25/ruby-2-7-0-released/
See also https://github.com/actions/virtual-environments/issues/95

[eregon]

Until Ruby 2.7.0 is supported here, https://github.com/eregon/use-ruby-action can be used for testing against Ruby 2.7.0 in GitHub Actions.

[maxim-lobanov]

Ruby 2.7 is available on Ubuntu images