Auto DevOps can't find pg gem

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

PG gem

The postgres gem cannot be found in the container that sets up the database. Pinning the version of either the pg gem, or ruby would probably fix this, but I can't find the correct versions documented.

== Preparing database ==
rails aborted!
LoadError: libruby.so.2.5: cannot open shared object file: No such file or directory - /app/vendor/bundle/ruby/2.5.0/gems/pg-1.1.2/lib/pg_ext.so
/app/vendor/bundle/ruby/2.5.0/gems/pg-1.1.2/lib/pg.rb:4:in `require'
/app/vendor/bundle/ruby/2.5.0/gems/pg-1.1.2/lib/pg.rb:4:in `<top (required)>'
/var/lib/gems/2.5.0/gems/bundler-2.0.1/lib/bundler/runtime.rb:81:in `require'
/var/lib/gems/2.5.0/gems/bundler-2.0.1/lib/bundler/runtime.rb:81:in `block (2 levels) in require'
/var/lib/gems/2.5.0/gems/bundler-2.0.1/lib/bundler/runtime.rb:76:in `each'
/var/lib/gems/2.5.0/gems/bundler-2.0.1/lib/bundler/runtime.rb:76:in `block in require'
/var/lib/gems/2.5.0/gems/bundler-2.0.1/lib/bundler/runtime.rb:65:in `each'
/var/lib/gems/2.5.0/gems/bundler-2.0.1/lib/bundler/runtime.rb:65:in `require'
/var/lib/gems/2.5.0/gems/bundler-2.0.1/lib/bundler.rb:114:in `require'
/app/config/application.rb:7:in `<top (required)>'
/app/Rakefile:4:in `require'
/app/Rakefile:4:in `<top (required)>'
/app/vendor/bundle/ruby/2.5.0/gems/railties-5.0.7/lib/rails/commands/rake_proxy.rb:13:in `block in run_rake_task'
/app/vendor/bundle/ruby/2.5.0/gems/railties-5.0.7/lib/rails/commands/rake_proxy.rb:11:in `run_rake_task'
/app/vendor/bundle/ruby/2.5.0/gems/railties-5.0.7/lib/rails/commands/commands_tasks.rb:51:in `run_command!'
/app/vendor/bundle/ruby/2.5.0/gems/railties-5.0.7/lib/rails/commands.rb:18:in `<top (required)>'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
(See full trace by running task with --trace)

== Command ["bin/rails db:setup"] failed ==

This failure is not easily diagnosed using the job output: https://gitlab.com/devin/license-gitlab-com/-/jobs/218943620