ci: Create test-docs job in mesa/mesa pipelines for MRs

Since the last GitLab update, pre-merge pipelines for MRs run in the
mesa/mesa namespace, so this job didn't get created anymore, causing
trouble.

Reviewed-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6522>
1 file changed