[FIX] account: only put internal users as followers of vendor bills created by emails

When the pdf of a vendor bill is sent to the alias of a journal,
all the partners that match one of the email address present in the mail thread
are added as followers of the newly created record.
This is a problem since the vendors are actually not concerned by the internal
work that is done, only internal users are.
As a result they get spammed by useless emails, and complain to Christine.
It was put in commit a4df9f8c93 despite not appearing in the task description.

We filter the partners to only keep the ones that belong to internal users.

opw 1958729

closes odoo/odoo#32110

Signed-off-by: Nans Lefebvre (len) <len@odoo.com>

addons/account/models/account_invoice.py

@@ -656,7 +656,7 @@ class AccountInvoice(models.Model):
         """
         # Split `From` and `CC` email address from received email to look for related partners to subscribe on the invoice
         subscribed_emails = email_split((msg_dict.get('from') or '') + ',' + (msg_dict.get('cc') or ''))
-        subscribed_partner_ids = [pid for pid in self._find_partner_from_emails(subscribed_emails) if pid]
+        seen_partner_ids = [pid for pid in self._find_partner_from_emails(subscribed_emails) if pid]
 
         # Detection of the partner_id of the invoice:
         # 1) check if the email_from correspond to a supplier
@@ -680,7 +680,7 @@ class AccountInvoice(models.Model):
 
         # If the partner_id can be found, subscribe it to the bill, otherwise it's left empty to be manually filled
         if partner_id:
-            subscribed_partner_ids.append(partner_id)
+            seen_partner_ids.append(partner_id)
 
         # Find the right purchase journal based on the "TO" email address
         destination_emails = email_split((msg_dict.get('to') or '') + ',' + (msg_dict.get('cc') or ''))
@@ -696,9 +696,13 @@ class AccountInvoice(models.Model):
         # Passing `type` in context so that _default_journal(...) can correctly set journal for new vendor bill
         invoice = super(AccountInvoice, self.with_context(type=values.get('type'))).message_new(msg_dict, values)
 
-        # Subscribe people on the newly created bill
-        if subscribed_partner_ids:
-            invoice.message_subscribe(subscribed_partner_ids)
+        # Subscribe internal users on the newly created bill
+        partners = self.env['res.partner'].browse(seen_partner_ids)
+        is_internal = lambda p: (p.user_ids and
+                                 all(p.user_ids.mapped(lambda u: u.user_has_groups('base.group_user'))))
+        partners_to_subscribe = partners.filtered(is_internal)
+        if partners_to_subscribe:
+            invoice.message_subscribe([p.id for p in partners_to_subscribe])
         return invoice
 
     @api.model