Gitlab: Avoid downloading all artifacts in later stages

Gitlab: Avoid downloading all artifacts in later stages

In the test.py stage of the build we mark the pytest results as
artifacts to save, so that they can be used for reports. This however
leads to all of the artifacts being downloaded (and then not used) in
later stages. Optimize this out by using an empty list of dependencies
here (which is the keyword for which artifacts are needed).

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