resolves the issue with the nixfiles being unable to be built, because
of a hash mismatch. The previous URL always pointed to the newest
version instead of a static one.
Sadly static links only exist for previous, but not the current version.
due to a wikiDB issue the mediawiki version in unstable (37) is not
compatible.
switching to 21.05 would mean a downgrade, so this is the hack until we
fully upgrade to 21.11
