revisions API: have release_revisions() release "date_mode"

revisions API: have release_revisions() release "date_mode"

Extend the the release_revisions() function so that it frees the
"date_mode" in the "struct ref_info".

This uses the date_mode_release() function added in 974c919d36d (date
API: add and use a date_mode_release(), 2022-02-16). As that commit
notes "t7004-tag.sh" tests for the leaks that are being fixed
here. That test now fails "only" 44 tests, instead of the 46 it failed
before this change.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>