I'm the original creator of that repo. Keeping it up to date is unfortunately a time-consuming manual effort. Doing version control downstream is generally a nightmare because unraveling different law changes/typo fixes is complicated (yes, lot's of typos when humans consolidate laws by hand).
If you're interested, here's a talk about it at Git Merge: https://www.youtube.com/watch?v=-qql1Ess7qM
Here are some scrapers/scripts around it: https://github.com/bundestag/gesetze-tools