[FIX] web, web_editor: ace widget partially hidden in read-only mode

Before this commit, the ´.ace_gutter´ overlapped the beginning
of the ace widget text content.

It only happens in read-only mode if it's a one-liner content.

Note that ´aria-hidden´ attribute is not set on BS modal. So,
it seems useless to remove it. Maybe a relicate of Bootstrap 3.

Steps to reproduce:
In debug mode,
- Open Settings
- Technical
- Scheduled Actions
- Open any

closes odoo/odoo#109346

Signed-off-by: Romeo Fragomeli (rfr) <rfr@odoo.com>