Replaced deprecated set-output

[lfgcampos]

What does this PR introduce?

• fixes [Bug] Usage of deprecated command #255

@benschwarz, I have to say I haven't tested it completely but the change seemed to be straightforward.
Sorry if I am missing something easy/stupid here =)

Reviewers

• @benschwarz

[lfgcampos]

hi @benschwarz, sorry to ping you on this but any news on it?

[benschwarz]

apologies for the delay @lfgcampos.

afaik you can use >> $GITHUB_OUTPUT (in bash) to push into the GITHUB_OUTPUT environment variable, but that isn't going to be a viable option from a node console log.

I think the path forward here would be to introduce @actions/core and the setOutput function, e.g.:

core.setOutput('markdown', escapedMarkdown);