t4014: clean up format.thread config after each test

The threading tests turn on format.thread, but never clean
up after themselves, meaning that later tests will also have
format.thread set.

This is more annoying than most leftover config, too,
because not only does it impact the results of other tests,
but it does so non-deterministically. Threading requires the
generation of message-ids, which incorporate the current
time, meaning a slow-running test script may generate
different results from run to run.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4014-format-patch.sh

@@ -445,22 +445,22 @@ test_expect_success 'thread deep cover-letter in-reply-to' '
 '
 
 test_expect_success 'thread via config' '
-	git config format.thread true &&
+	test_config format.thread true &&
 	check_threading expect.thread master
 '
 
 test_expect_success 'thread deep via config' '
-	git config format.thread deep &&
+	test_config format.thread deep &&
 	check_threading expect.deep master
 '
 
 test_expect_success 'thread config + override' '
-	git config format.thread deep &&
+	test_config format.thread deep &&
 	check_threading expect.thread --thread master
 '
 
 test_expect_success 'thread config + --no-thread' '
-	git config format.thread deep &&
+	test_config format.thread deep &&
 	check_threading expect.no-threading --no-thread master
 '