Replace deprecated `set-output` command

[nandahkrishna]

See here: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

TL;DR: The set-output command has been deprecated and we should be writing to the $GITHUB_OUTPUT environment file instead.

Old syntax:

- name: Set output
  run: echo "::set-output name={name}::{value}"

New syntax:

- name: Set output
  run: echo "{name}={value}" >> $GITHUB_OUTPUT

[nandahkrishna]

Merging since the comment was addressed.

[Bo98]

Looks good, thanks!