t5510: do not leave changed cwd

t5510 carefully keeps the cwd at the test root by using either subshells
or explicit cd'ing back to the root. Use a subshell for the last
subtest, too.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5510-fetch.sh

@@ -679,10 +679,12 @@ test_expect_success 'fetching with auto-gc does not lock up' '
 	EOF
 	git clone "file://$D" auto-gc &&
 	test_commit test2 &&
+	(
 		cd auto-gc &&
 		git config gc.autoPackLimit 1 &&
 		GIT_ASK_YESNO="$D/askyesno" git fetch >fetch.out 2>&1 &&
 		! grep "Should I try again" fetch.out
+	)
 '
 
 test_done