CI/CD: console warning on set-output command deprecation

[mfranzke]

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/

e.g. https://github.com/db-ui/elements/actions/runs/3326919748