diff tests: don't ignore "git rev-list" exit code

Change a fragile pattern introduced in 2b459b4 (diff: make sure
work tree side is shown as 0{40} when different, 2008-03-02) to check
the exit code of "git rev-list", while we're at it let's get rid of
the needless sub-shell for invoking it in favor of the "-C" option.

Because of this I'd marked these tests as passing under SANITIZE=leak
in 16d4bd4 (leak tests: mark some diff tests as passing with
SANITIZE=leak, 2021-10-31), let's remove the
"TEST_PASSES_SANITIZE_LEAK=true" annotation as they no longer do.

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

Author: avar

t/t4027-diff-submodule.sh

@@ -2,7 +2,6 @@
 
 test_description='difference in submodules'
 
-TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-diff.sh
 
@@ -28,10 +27,8 @@ test_expect_success setup '
 		git commit -m "submodule #2"
 	) &&
 
-	set x $(
-		cd sub &&
-		git rev-list HEAD
-	) &&
+	git -C sub rev-list HEAD >revs &&
+	set x $(cat revs) &&
 	echo ":160000 160000 $3 $ZERO_OID M	sub" >expect &&
 	subtip=$3 subprev=$2
 '