t3070: make chain lint tester happy

1f2e05f0b7 ("wildmatch: fix exponential behavior", 2023-03-20)
introduced a new test with a background process. Backgrounding
necessarily gives a result of 0, so that a seemingly broken && chain is
not really broken.

Adjust t3070 slightly so that our chain lint test recognizes the
construct for what it is and does not raise a false positive.

Signed-off-by: Michael J Gruber <git@grubix.eu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3070-wildmatch.sh

@@ -432,10 +432,12 @@ match 0 1 0 1 'z' '[Z-y]'
 match 1 1 1 1 'Z' '[Z-y]'
 
 test_expect_success 'matching does not exhibit exponential behavior' '
-	test-tool wildmatch wildmatch \
-		aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab \
-		"*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a" &
-	pid=$! &&
+	{
+		test-tool wildmatch wildmatch \
+			aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab \
+			"*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a" &
+		pid=$!
+	} &&
 	sleep 2 &&
 	! kill $!
 '