.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)
Status Job ID Name Coverage
  Docker Image
passed #9789014
debian-buster

00:14:03

 
  Build And Test
passed #9789015
autotools

00:07:00

passed #9789016
meson

00:03:44

passed #9789017
meson-noglamor

00:03:09

passed #9789018
mingw-cross-build

00:01:05