Examples use deprecated set-output

[anselmbradford]

If you look at the examples at https://github.com/actions/cache/blob/master/examples.md#node---yarn, they are using set-output, which is deprecated. See https://github.blog/changelog/2023-07-24-github-actions-update-on-save-state-and-set-output-commands/

These examples should be updated to use envvars.