fix(license): only return the license in pro mode

builder/steps/return_license.sh

@@ -1,5 +1,6 @@
 #!/usr/bin/env bash
 
+if [[ -n "$UNITY_SERIAL" ]]; then
   #
   # PROFESSIONAL (SERIAL) LICENSE MODE
   #
@@ -12,3 +13,4 @@ xvfb-run --auto-servernum --server-args='-screen 0 640x480x24' \
       -logFile /dev/stdout \
       -quit \
       -returnlicense
+fi