modified: checkout.sh to check out model tag GFS.v16.0.3

            In Sfc_diff.f, a bug was introduced when the surface layer scheme was
            updated last time to reduce 2-m temperature cold biases.   The bug only
            has impact over sea-ice points, where momentum and thermal roughness
            are nevertheless very small.

sorc/checkout.sh

@@ -9,7 +9,7 @@ if [[ ! -d fv3gfs.fd ]] ; then
     rm -f ${topdir}/checkout-fv3gfs.log
     git clone https://github.com/ufs-community/ufs-weather-model fv3gfs.fd >> ${topdir}/checkout-fv3gfs.log 2>&1
     cd fv3gfs.fd
-    git checkout  GFS.v16.0.2
+    git checkout  GFS.v16.0.3
     git submodule update --init --recursive
     cd ${topdir}
 else