The current MediaWiki link check misses a few Markdown-style relative BIP links, for example:
[text](bip-0340.mediawiki)[text](./bip-0340.mediawiki)[text](../../bip-0340.mediawiki)
Because of that, these links can pass CI even though they use Markdown syntax inside a .mediawiki file.
This updates the existing regex so relative BIP links are caught consistently, including ./, ../, deeper parent paths, and root-relative paths.
Valid MediaWiki links are unaffected.