* Check git version before attempting to disable `sparse-checkout`
* Bump `MinimumGitSparseCheckoutVersion` to 2.28 due to #1386
* Initial prep for release 4.1.3
* Give `test-ubuntu-git` its own `README`
* Refined title and description in `test-ubuntu-git.Dockerfile`
* nit accepted: Remove double space
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Co-authored-by: Ferenc Hammerl <31069338+fhammerl@users.noreply.github.com>