API key is requested from shell output even when not needed

[schneems]

From this test https://github.com/heroku/heroku-buildpack-ruby-experimental/blob/d5e3b25361cf39cf8077a335017c8d38c5e69dfe/spec/unit/assets_precompile_spec.rb#L8-L33

We can see the bulk of time is spent getting the API token.

Even if it's just a few seconds, that creates a minimum cycle time for that test file.