Fix CI warning by removing set-output command

[mast-eu]

This PR is to fix some warnings which I noticed in the CI jobs "compile-test":

The fix is straight-forward and described in the link given in the warning: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

All occurrences of

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

should be replaced by

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

The other deprecated command is save-state, which is not used here.

[per1234]

Thanks @mast-eu!