[FIX] web_editor: prevent inline snippet drop in non-inline area

Before this commit, it was possible to drop an inline snippet (e.g.
badge, cards, etc.) next to a section when this section was a snippet
which can be dropped as main snippets or as inline snippets (e.g.
countdown, embed code, etc.).

task-2648348

closes odoo/odoo#76827

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>