ci: Use GITHUB_OUTPUT envvar instead of set-output command

[arunsathiya]

save-state and set-output commands used in GitHub Actions are deprecated and GitHub recommends using environment files.

This PR updates the usage of ::set-output to "$GITHUB_OUTPUT"

Instructions for envvar usage from GitHub docs:

https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter

[github-actions[bot]]

PR is now waiting for a maintainer to take action.

Note for the maintainer: Commands available:

• /run-acceptance-tests - used to test run the acceptance tests for the project

[justinvp]

Thanks!