[gz-sim] Skip in CI

[BillyONeal]

We are regularly seeing this port cause other folks' PRs to fail. Even when it succeeds we are getting warnings like: https://dev.azure.com/vcpkg/public/_build/results?buildId=126597

Installing 1196/2727 gz-sim:x64-linux@9.5.0...
Building gz-sim:x64-linux@9.5.0...
Trying to download ignitionrobotics-ign-gazebo-gz-sim9_9.5.0-1.tar.gz using asset cache https://vcpkgassetcachewus.blob.core.windows.net/cache/45125f324d65114264bb57afb99b11f3dab6110f95dad673ec992735c1c958b8fff2daefe90465b3b731499adac8a7e8e790c2a8cbf1e1d73a75ad8362ea4d43?*** SECRET ***
Download successful! Asset cache hit, did not try authoritative source https://github.com/ignitionrobotics/ign-gazebo/archive/gz-sim9_9.5.0.tar.gz
-- Extracting source /vcpkg/downloads/ignitionrobotics-ign-gazebo-gz-sim9_9.5.0-1.tar.gz
-- Applying patch dependencies.patch
-- Using source at /mnt/vcpkg-ci/b/gz-sim/src/sim9_9.5.0-89c77b8d6c.clean
-- Configuring x64-linux-dbg
-- Configuring x64-linux-rel
-- Building x64-linux-dbg
##[warning]Free memory is lower than 5%; Currently used: 95.55%
##[warning]Free memory is lower than 5%; Currently used: 95.55%
##[warning]Free memory is lower than 5%; Currently used: 95.55%
##[warning]Free memory is lower than 5%; Currently used: 95.55%

Given that there seem to be relatively few users of this port, and the version we have is already substantially out of date anyway, I'm proposing to skip it in CI.