fix(nginxproxymanager): unmask openresty after migration from package

When migrating from packaged OpenResty to source-built, apt remove
masks the service unit. This causes systemctl restart to fail after
the build completes.

Closes #13373

ct/nginxproxymanager.sh

@@ -93,6 +93,7 @@ ExecStart=/usr/local/openresty/nginx/sbin/nginx -g 'daemon off;'
 WantedBy=multi-user.target
 EOF
     systemctl daemon-reload
+    systemctl unmask openresty 2>/dev/null || true
     systemctl restart openresty
     msg_ok "Built OpenResty"
   fi