We have been moving our infrastructure to Git v2.29.0, so we can now
finally require use of that or a higher version. This is done to allow
us to make use of the following features:

- Split commit graphs, which have been introduced with Git v2.27.0.
  These allow more efficient creation of commit-graphs to speed up
  various operations on Git version history.

- Reference transaction hook, introduced with Git v2.28.0 and fixed with
  Git v2.29.0. This is required to implement strong consistency used by
  Gitaly and Praefect for all reference updates in a Git repository.