`set-output` function is deprecated

[jrfnl]

Description

GitHub in their wisdom has deprecated the use of set-output (and save-state). As set-output is used in every script in this action runner, the logs of any workflow run using it are now showing lots of warnings.

Refs:

• https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
• https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter

Expected behavior

No warnings.

Screenshots or output

Environment details

Not relevant

Additional context

I've got the principle for a fix ready, just running into issues with the tests as expect doesn't show the new output, so I'm not all that sure what the updated output expectations should be.

[jrfnl]

Looks like PR #235 attempts to address this and that @desrosj has got the test updates figured out already.