checkInputs used to be added to nativeBuildInputs. Now we have
nativeCheckInputs to do that instead. Doing this treewide change allows
to keep hashes identical to before the introduction of
nativeCheckInputs.
Build was broken as release-0.6.0 didn't support opentimestamps-0.4.0.
Applying the patch which relaxes the version contraints in `setup.py`
helps.
Furthermore the tests were broken as they missed the `git` executable.