Fix shellcheck issues

[Doommius]

fixed some issues from https://www.shellcheck.net that were given issues in pipelines using it.

What does this change

Fixed linting issues presented by shellcheck

What issue does it fix

linting issue.

Notes for the review

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

[schristoff]

Thank you for this PR! Please don't forget to add yourself to the contributors file :)