[CI] NPM script `check:links--md` no longer working

[chalin]

It first started failing under GH's Ubuntu, but it is now failing locally for me too (macOS):

$ npm run check:links--md                    

> docsy@0.11.1-dev-unreleased check:links--md
> ls *.md | xargs npx markdown-link-check --config .markdown-link-check.json

FILE: CHANGELOG.md

FILE: CONTRIBUTING.md

FILE: README.md
$ echo $?                
1

There's an issue with markdown-link-check.

Might it be time to tackle #1781 ? :)

[chalin]

By using the --progress flag, I can see that indeed some link checks are failing, such as:

 [✖] https://badges.netlify.com/api/docsydocs.svg?branch=main

But the link-check failures aren't being reported. :-/

[chalin]

Temporary workaround:

• 2118