First of all, thank you for this action! It's been very useful.

I noticed while using it that it's using set-output internally, which has been deprecated by GitHub:

The set-output command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

GitHub's encouraged alternative is to use the $GITHUB_OUTPUT file, e.g.:

echo "foo=bar" >> "${GITHUB_OUTPUT}"

I'm not super familiar with Go, but I suspect you're using the deprecated set-output command indirectly through this line:

...and that upgrading to 1.1.0 or newer will fix the underlying implementation, per sethvargo/go-githubactions#49