pytest: Update requirements to match sphinx versions

In order to better make use of pip caches, and also for better overall
consistency, we should use the same versions of packages in each of our
python requirements files. Update pytest to use the newer versions of
packages we use in sphinx builds.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>