GHA: replace last plain text server name for variable

one of the server urls was left as code, replaced with github variable

Signed-off-by: Robert Gałat <[email protected]>

.github/workflows/publish_documentation.yml

@@ -74,7 +74,7 @@ jobs:
       - name: Prepare Key
         run: |
           mkdir -p /root/.ssh
-          ssh-keyscan upload-v1.zoominsoftware.io >> /root/.ssh/known_hosts
+          ssh-keyscan ${{ vars.NCS_ZOOMIN_SERVER }} >> /root/.ssh/known_hosts
           echo "${{ secrets.NCS_ZOOMIN_KEY }}" > zoomin_key
           chmod 600 zoomin_key