Stop using deprecated set-output in GitHub Action workflows

[jeffcharles]

Description of the change

Uses the updated syntax for setting step outputs.

Why am I making this change?

We're getting deprecation warnings using the current syntax. See https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/.

Checklist

• [x] I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli and javy-plugin do not require updating CHANGELOG files.
• [x] I've updated the relevant crate versions if necessary. Versioning policy for library crates
• [x] I've updated documentation including crate documentation if necessary.