t2017: mark --orphan/logAllRefUpdates=false test as REFFILES

In reftable, there is no notion of a per-ref 'existence' of a reflog. Each
reflog entry has its own key, so it is not possible to distinguish between
{reflog doesn't exist,reflog exists but is empty}. This makes the logic
in log_ref_setup() (file refs/files-backend.c), which depends on the existence
of the reflog file infeasible.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Reviewed-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t2017-checkout-orphan.sh

@@ -76,7 +76,7 @@ test_expect_success '--orphan makes reflog by default' '
 	git rev-parse --verify delta@{0}
 '
 
-test_expect_success '--orphan does not make reflog when core.logAllRefUpdates = false' '
+test_expect_success REFFILES '--orphan does not make reflog when core.logAllRefUpdates = false' '
 	git checkout main &&
 	git config core.logAllRefUpdates false &&
 	git checkout --orphan epsilon &&