Auto DevOps can't pin ruby version

Currently, an arbitrary Rails app cannot be deployed using Auto DevOps. It's likely that some combination of ruby, rails, bundler, postgres client and devise gem will work, but this is not documented anywhere that I could find.

Here are the pipeline failures I've been getting: https://gitlab.com/devin/license-gitlab-com/pipelines

Ruby

The build phase has a warning:

You have not declared a Ruby version in your Gemfile.
       To set your Ruby version add this line to your Gemfile:
       ruby '2.5.3'

However, pinning the ruby version breaks the review deployment. Pods fail with an error about ruby version mismatch in the Kubernetes logs (2.5.3 vs 2.5.1).

https://gitlab.com/devin/license-gitlab-com/-/jobs/216743526