pytest: update requirements.txt

Update pygit2 and py to their latest versions. Even in the venv pygit2
still links against the system libgit2 library which is failing on
latest Arch Linux.

The py library also needs updating to fix a KeyNotFound exception during
test initialisation.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
1 file changed