Update output syntax

[amannn]

Is your feature request related to a problem? Please describe.

Seems like GitHub has changed the syntax for setting an output variable: https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter

Describe the solution you'd like

Use the new syntax

Describe alternatives you've considered

Keep using the current syntax until it's deprecated