Use variable for product name (#18903)

Author: mattpollard

content/github/authenticating-to-github/using-ssh-over-the-https-port.md

@@ -11,7 +11,7 @@ topics:
 
 {% tip %}
 
-**GitHub Enterprise users**: Accessing GitHub Enterprise via SSH over the HTTPS port is currently not supported.
+**{% data variables.product.prodname_ghe_server %} users**: Accessing {% data variables.product.prodname_ghe_server %} via SSH over the HTTPS port is currently not supported.
 
 {% endtip %}