Steps to reproduce
==================
1. Open course with enroll policy onInvitation or
Click on three dot of any course in kanban view
2. Click on Invite > add a recipient
3. Go to mail template internal link
4. Go to setting tab
5. Disable the 'Auto delete' > save & close it
6. Click on Send
7. Go the Technical/Emails (in debug mode)
8. Send the mail by clicking 'Send now'
Issue - Even if we unchecked auto delete still the mail is deleted automatically
Technical
=========
In the '_prepare_mail_values' method of the 'slide.channel.invite' model, the
mail values for 'mail.mail' are prepared and the auto delete is set to True.
After this commit
=================
You can view the sent mails since the auto_delete is configured based on
the template value for invitation.
Task-3546212
closesodoo/odoo#141141
X-original-commit: 3d9640d5c24f345d67e4e74e62584e60cc27815b
Signed-off-by: Warnon Aurélien (awa) <awa@odoo.com>