arch-nspawn: Enable --suppress-sync=yes

Should improve container performance when tmpfs is not in use.

arch-nspawn.in

@@ -125,6 +125,6 @@ fi
 exec ${CARCH:+setarch "$set_arch"} systemd-nspawn -q \
 	-D "$working_dir" \
 	-E "PATH=/usr/local/sbin:/usr/local/bin:/usr/bin" \
-	--register=no --keep-unit --as-pid2 \
+	--register=no --keep-unit --as-pid2 --suppress-sync=yes \
 	"${mount_args[@]}" \
 	"$@"