Ignore HTTP response 429 during link check

Ignore HTTP respone error code 429: Too Many Requests when link-checking
markdown files.

Some sites, such as Medium, return this error code even though the link
is live. Presumably, Medium does this for "members-only" articles.
Example:

https://betterprogramming.pub/text-to-audio-generation-with-bark-clearly-explained-4ee300a3713a

See also:

https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/429

.github/scripts/markdown_link_check_config.json

@@ -23,5 +23,6 @@
     {
       "pattern": "https://www.intel.com/content/www/us/en/developer/articles/news/llama2.html"
     }
-  ]
+  ],
+  "aliveStatusCodes": [429, 200]
 }