t5520: do not use pull.rebase=preserve

Even if those tests try to override that setting, let's not use it
because it is deprecated: let's use `merges` instead.

Signed-off-by: Johannes Schindelin <[email protected]>
Reviewed-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dscho

t/t5520-pull.sh

@@ -598,7 +598,7 @@ test_expect_success '--rebase=false create a new merge commit' '
 
 test_expect_success '--rebase=true rebases and flattens keep-merge' '
 	git reset --hard before-preserve-rebase &&
-	test_config pull.rebase preserve &&
+	test_config pull.rebase merges &&
 	git pull --rebase=true . copy &&
 	test_cmp_rev HEAD^^ copy &&
 	echo file3 >expect &&
@@ -620,9 +620,9 @@ test_expect_success '--rebase=invalid fails' '
 	test_must_fail git pull --rebase=invalid . copy
 '
 
-test_expect_success '--rebase overrides pull.rebase=preserve and flattens keep-merge' '
+test_expect_success '--rebase overrides pull.rebase=merges and flattens keep-merge' '
 	git reset --hard before-preserve-rebase &&
-	test_config pull.rebase preserve &&
+	test_config pull.rebase merges &&
 	git pull --rebase . copy &&
 	test_cmp_rev HEAD^^ copy &&
 	echo file3 >expect &&