Update update_NDM.yml

only run if git diff is not empty

.github/workflows/update_NDM.yml

@@ -23,14 +23,14 @@ jobs:
             svn export --force https://vlab.noaa.gov/svn/awips-ndm/trunk/"$file" --username ${{ secrets.VLAB_UNAME }} --password ${{ secrets.VLAB_PASS }}
           done
       # Check in all the new files
-      # Do we need to check for a change or can we just run a git add?
+      # Only do a git add/commit/push if files have changed
       - name: Update existing NDM files for awips2 repo
         run: |
           date=`date +%Y%m%d-%H:%M:%S`
           git config user.name $GITHUB_ACTOR
           git config user.email $GITHUB_ACTOR@users.noreply.github.com
           change=`git diff`
-          if [ -z "$change" ]
+          if [ "$change" -ge 1 ]
           then
             git add --all
             git commit -m "New NDM updates on $date - autogenerated"