[FIX] *: some border aren't apply anymore

* = digest, hw_posbox_homepage, im_livechat, mass_mailing, pow_cache,
web_editor, website, website_slides_forum

Since the migration of Bootstrap 5 [1], some CSS rules was automatically
converted (`border-left` and `border-right`) when it shouldn't be.
These conversions were made because the CSS rules was embedded in
HTML/XML code and the REGEX for the conversion had no protection for
these cases.

This commit restores the old correct value.

Ref:
[1] odoo/odoo@1fcd098af5fa18e848c66bb83bdceb6ba0308512

closes odoo/odoo#109861

Signed-off-by: Adrien Dieudonné (adr) <adr@odoo.com>