protocol/meson.build: Bump wayland-protocol requirement to 1.18

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
2 jobs for wip/w-p-1-18 in 1 minute and 22 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Container Prep
passed #467851
container_prep

00:00:27

 
  Build
passed #467852
build-native-meson

00:00:54