.gitlab-ci: Install xorgproto 2021.4.99.1 from git

This is required for the support of upcoming XI 2.4 protocol.

Signed-off-by: Povilas Kanapickas <povilas@radix.lt>
5 jobs for xorgproto-2021.4.99.1 in 21 minutes and 4 seconds (queued for 2 seconds)