Keep /root permissions as 750

The filesystem package installs /root as 750 not 700.

Move chmod from customize_airootfs.sh to build.sh.

configs/releng/airootfs/root/customize_airootfs.sh

@@ -7,7 +7,6 @@ locale-gen
 
 usermod -s /usr/bin/zsh root
 cp -aT /etc/skel/ /root/
-chmod 700 /root
 # unset the root password
 passwd -d root
 

configs/releng/build.sh

@@ -131,6 +131,8 @@ make_customize_airootfs() {
             -r '/root/customize_airootfs.sh' run
     fi
     rm "${work_dir}/x86_64/airootfs/root/customize_airootfs.sh"
+
+    chmod -f 750 "${work_dir}/x86_64/airootfs/root"
 }
 
 # Prepare kernel/initramfs ${install_dir}/boot/