[FIX] mail: make default mode for channel 'groups', not 'public'

It's currently confusing: the default value is already 'groups', but the create
method is actually giving another default.

task-2749643

closes odoo/odoo#86075

X-original-commit: 31dfc797bc0fb163b6e32d3fe2195791b674f00c
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/models/mail_channel.py

@@ -1065,7 +1065,7 @@ class Channel(models.Model):
         self.add_members(self.env.user.partner_id.ids)
 
     @api.model
-    def channel_create(self, name, privacy='public'):
+    def channel_create(self, name, privacy='groups'):
         """ Create a channel and add the current partner, broadcast it (to make the user directly
             listen to it when polling)
             :param name : the name of the channel to create

addons/mail/static/src/models/discuss/discuss.js

@@ -40,7 +40,7 @@ registerModel({
                 const channel = await this.async(() =>
                     this.messaging.models['Thread'].performRpcCreateChannel({
                         name,
-                        privacy: ui.item.special,
+                        privacy: ui.item.special === 'private' ? 'private' : 'groups',
                     })
                 );
                 channel.open();