Do not print unsupported mixin command errors

[carolynvs]

What does this change

Not all of the mixin commands are required, for example schema and lint are optional. Porter does ignore failed commands when the mixin doesn't support a called command, but after I updated that bit of code to use spans and structured logging, I accidentally caused porter to always print out if the command failed, even when the verbosity is greater than debug.

This fixes failed mixin commands to only print the error when verbosity is debug and I've added a CLI test to validate that we print when expected to avoid future regressions in this area.

What issue does it fix

#2487

Notes for the reviewer

N/A

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR