yes: fix argv test race between fork and exec

The argv test checks ps(1) output immediately after backgrounding yes(1), but
the forked child briefly shows the parent shell's argv before exec(2) replaces it.
This caused intermittent failures where ps(1) captured the atf shell wrapper
command line instead of "yes y".

Approved by:	des
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D56231

usr.bin/yes/tests/yes_test.sh

@@ -52,6 +52,8 @@ argv_body()
 {
 	yes y >/dev/null &
 	local pid=$!
+	# Wait for yes(1) to exec before checking args
+	sleep 0.1
 	atf_check -o inline:"yes y\n" ps -o args= $pid
 	kill $pid
 	wait