bug#40144: --rounds has no effect when used in conjunction with --check

[Brice Waegeneire]

Hello,

Since this bug is already known[0] this report is just to keep of it.

“guix --check --rounds=3 hello” only build the package once instead of
three time.

[0]: http://logs.guix.gnu.org/guix/2020-03-18.log#213921

Brice.