package/x11r7/xorgproto: bump version to 2021.4

Release notes:
https://lists.x.org/archives/xorg-announce/2021-April/003085.html



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>