build: annotate markdown lint failures in pull requests

Add a problem matcher for output from remark-lint to our lint-md GitHub
Actions CI workflow so that any markdown linter failures are annotated
in the pull request in the web UI.

Signed-off-by: Richard Lau <riclau@uk.ibm.com>

PR-URL: https://github.com/nodejs/node/pull/32391
Refs: https://github.com/actions/toolkit/blob/master/docs/problem-matchers.md
Refs: https://github.com/actions/toolkit/blob/master/docs/commands.md#problem-matchers


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>