setup: exclude the git extension from py2 builds
This can't be built on Windows with the py2 compiler, and while old versions can
be installed via pip on Linux, I can't get the tests to run (even with py3.8)
using pygit2 0.28.2. Some manually run commands work, and others spew stack
traces that don't occur with the current 1.4.0 release using py3.
Differential Revision: https://phab.mercurial-scm.org/D9604
This directory is meant to cache artifacts useful for tests (such as bundle).
Those artifacts need to be cached because they are slow to regenerate on each
test but too large to be tracked within the repository. They are not expected
to change between each run and can be cached.
The `./scripts/` contains code to generate the artifact while the `cache`
directory contains resulting artifact.