Bump version to 21.0.99.902

Xwayland 21.1.0 release candidate 2.
3 jobs for xwayland-21.0.99.902 in 2 minutes and 27 seconds
Status Job ID Name Coverage
  Docker Image
passed #7722675
debian-buster

00:00:21

 
  Build And Test
passed #7722676
meson

00:01:57

passed #7722677
meson-noglamor

00:02:06