[FIX] web_editor: link with @ open new window option

Before this commit, when using the LinkTools (website, mass_mailing),
if an http URL contained a "@" (ex: https://www.youtube.com/@iRopes

),
it got incorrectly recognized as an e-mail URL and the option to open
the link in a new windown was hidden from the UI.

This commit fixes the issue by making the test for e-mail URL slightly
more robust than just checking for the presence of a "@".

task-3356685
opw-3349704

closes odoo/odoo#124110

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>