scripts/test: make MacOS compatible

scripts/test: make MacOS compatible

man xargs:
     -r      Compatibility with GNU xargs.  The GNU version of xargs runs the utility argument at least once, even if xargs input is empty, and it supports a -r option to inhibit this
             behavior.  The FreeBSD version of xargs does not run the utility argument on empty input, but it supports the -r option for command-line compatibility with GNU xargs, but the
             -r option does nothing in the FreeBSD version of xargs.