The "set-output" command is deprecated

[kenorb]

Compile workflow needs some fixes as per error:

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/

See also:

• https://matthewrich.com/2022/10/13/github-actions-job-output/
• https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#environment-files

Branch with attempted fix: dev-ci-fixme (see: a84f6e9).

The problem is, that we're trying to set GITHUB_OUTPUT from Python which doesn't work, see: https://stackoverflow.com/questions/5971312/how-to-set-environment-variables-in-python.