[changelog skip] Remove Heroku-16 from tests: (#1146)
[changelog skip] Remove Heroku-16 from tests: (#1146)

```
Hatchet::App::FailedDeployError: Could not deploy 'hatchet-t-5e1aedd6a2' (default_ruby) using 'Hatchet::GitApp' at path: 'test/fixtures/repos/ruby/default_ruby'
if this was expected add `allow_failure: true` to your deploy hash.
Buildpack: nil
Repo: https://git.heroku.com/hatchet-t-5e1aedd6a2.git
output:
remote: Compressing source files... done.
remote: Building source:
remote:
remote: !   Your app is using the Heroku-16 stack, which will be end-of-life on May 1st, 2021.
remote: !
remote: !   Builds on Heroku-16 will not be possible from June 1st, 2021.
remote: !
remote: !   Please upgrade the stack of your app as soon as possible:
remote: !   https://devcenter.heroku.com/articles/upgrading-to-the-latest-stack
remote: !
remote: !   Heroku-16 EOL FAQ: https://help.heroku.com/0S5P41DC/heroku-16-end-of-life-faq
remote: !
remote: !   THIS IS A ONE-OFF NOTICE. THE NEXT DEPLOY WILL FUNCTION WITHOUT INTERRUPTION.
remote: !
remote: !   The next warning of this kind will occur in: 7 day(s).
remote:
To https://git.heroku.com/hatchet-t-5e1aedd6a2.git
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```
brightbytes/heroku-buildpack-ruby-without-assets-precompile,brightbytes/heroku-buildpack-ruby-without-assets-precompile,Scalingo/ruby-buildpack,instacart/heroku-buildpack-ruby,instacart/heroku-buildpack-ruby,Genius/heroku-buildpack-ruby,heroku/heroku-buildpack-ruby,heroku/heroku-buildpack-ruby,Scalingo/ruby-buildpack,Genius/heroku-buildpack-ruby