Version related mismatches - guide is not up to date with MIxS version

As mentioned [here](https://github.com/tdwg/gbwg/issues/83#issuecomment-3396598811):

> One key finding from the mapping was the presence of version-related mismatches. The DNA-derived data extension shows several syntactic inconsistencies, as MIxS has already moved to version 6 and will soon be moving toward version 7.