selftests: harness: Use C89 comment style

All comments in this file use C89 comment style.
Except for this one. Change it to get one step closer to C89
compatibility.

Signed-off-by: Thomas Weißschuh <[email protected]>
Acked-by: Shuah Khan <[email protected]>
Link: https://lore.kernel.org/r/20250505-nolibc-kselftest-harness-v4-2-ee4dd5257135@linutronix.de
Signed-off-by: Thomas Weißschuh <[email protected]>

Author: t-8ch

tools/testing/selftests/kselftest_harness.h

@@ -983,7 +983,7 @@ static void __timeout_handler(int sig, siginfo_t *info, void *ucontext)
 	}
 
 	t->timed_out = true;
-	// signal process group
+	/* signal process group */
 	kill(-(t->pid), SIGKILL);
 }