[FIX] website_slide: fix improper display of values

Before this commit, some tag would not display correctly in the tag list of eLearning

This commit fixes this behavior

closes odoo/odoo#108041

closes odoo/odoo#111692

Related: odoo/enterprise#35003
Signed-off-by: Vranckx Florian (flvr) <flvr@odoo.com>