install the latest vulkan sdk from tarball

lunarg no longer updates ubuntu packages, and those are stale

render/rendertest.py

@@ -150,7 +150,7 @@ def render():
 	print('Running xash3d...')
 	mkdir_p(f'{args.xash_dir}/valve/rendertest')
 	env = os.environ.copy()
-	env['LD_LIBRARY_PATH'] = f'{args.xash_dir}'
+	env['LD_LIBRARY_PATH'] = f'{args.xash_dir}:{env["LD_LIBRARY_PATH"]}'
 
 	start_time_sec = time.perf_counter()
 	with open(f'{WORKDIR}/xash-stdout.log', 'wb') as stdout, open(f'{WORKDIR}/xash-stderr.log', 'wb') as stderr: