build_manifest.py: Gitlab search API returned paged results

Consider the following query: https://gitlab.freedesktop.org/api/v4/users/slomo/projects?search=gstreamer

When I run it locally I got back 19 results, and none of which where the gstreamer core fork.

There might be a header we can set to get the full output?

Opening the issue so I won't forget mostly.