Fix check_pid() in runtime system test on FreeBSD

The original check_pid() always returned 0 on FreeBSD, even if the
process was still running. This makes the "verifying that named checks
for conflicting named processes" check fail on FreeBSD with TSAN.

(cherry picked from commit 6acaca963d)

bin/tests/system/runtime/tests.sh

@@ -62,7 +62,7 @@ run_named() (
 )
 
 check_pid() (
-  return $(! kill -0 "${1}" >/dev/null 2>&1)
+  ! kill -0 "${1}" >/dev/null 2>&1
 )
 
 status=0