gitlab-ci: Use publish to specify artifacts path for pages

By default, gitlab pages assumes that we want to publish the content of the "public" folder. Since this one no longer exists, the publish job fails.

Add a "publish" keyword as recommended by the doc [1]

[1] https://docs.gitlab.com/ee/ci/yaml/#pagespublish Signed-off-by: Mattijs Korpershoek mkorpershoek@baylibre.com