tests: fix comment syntax in chainlint.sed for AIX sed

Change a comment in chainlint.sed to appease AIX sed, which would
previously print this error:

    sed:    # stash for later printing is not a recognized function

1. https://public-inbox.org/git/CAPig+cTTbU5HFMKgNyrxTp3+kcK46-Fn=4ZH6zDt1oQChAc3KA@mail.gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Acked-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/chainlint.sed

@@ -131,9 +131,8 @@ b
 b
 
 :subshell
-# bare "(" line?
+# bare "(" line? -- stash for later printing
 /^[ 	]*([	]*$/ {
-	# stash for later printing
 	h
 	bnextline
 }