Before this commit, since there is a mildly transparent filter over the
entire view when the "no content" helper is displayed, the interactive
elements of the empty kanban view (namely: the title with the name and
"quick create" button) were slightly hidden.
This commit enforces a superior z-index on those elements s.t. they can
appear on top of the helper's filter.
closesodoo/odoo#105140
X-original-commit: cbefc9cd51b3c903a6c54d8e3f95bf2b592cf402
Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>