[FIX] website_slides: prevent auto-marking videos complete

When user will open the video in any course, it will be marked as completed
directly which behaves like any other content(pdf, image). This behavior was
introduced when 'slide_view' was modified in https://github.com/odoo/odoo/commit/4c291fe30468dab7cef9d2e5a0377c78484f5045

, but in the case of video,
it must not be marked as completed before the video is watched up until(near)
the end, as per the previous behavior.

Task-3346507

closes odoo/odoo#124123

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>