ci: Do not create manual test-docs job in post-merge pipelines

Only in pre-merge pipelines for MRs, or in pipelines for forked project
branches.

Having the manual job in post-merge pipelines prevented the pages job
from running automatically as well, which could prevent the public
website from getting updated.

Acked-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6534>
1 file changed