Fix set-output deprecation warning

[pbek]

e.g. https://github.com/pbek/QOwnNotes/actions/runs/3394387148

Create release
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/

• 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