Fix unbroken checks for npmjs.com URLs hitting 403

[sundaramramaswamy]

When queried npmjs.com URLs are queried from GitHub CI machines or from Microsoft's network (perhaps behind its proxies) fail with 403 Forbidden Request. Trying to add enough headers don't help too

$ curl -A "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/116.0.0.0 Safari/537.36" \
  -H "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8" \
  -H "Accept-Language: en-US,en;q=0.9" \
  -H "Accept-Encoding: gzip, deflate, br" \
  --compressed \
  -L \
  -I \
  https://www.npmjs.com/

HTTP/2 403

These URLs are deemed broken by unbroken, thereby leading to documentation fixing PRs getting blocked due to these false positives.

[sundaramramaswamy]

Adding exceptions to .unbroken_exclusions is a workaround. Once asklar/unbroken#40 is fixed, these exceptions should be removed.