[FIX] purchase: send email on RFQ confirmation

When confirming a RfQ, even if a follower is subscribed to "RFQ
Confirmed", he will not receive any email.

To reproduce the error:
(Need a mail catcher)
1. Create a PO
2. Add a follower and edit his subscriptions:
    - Check 'RFQ Confirmed'
3. Confirm the PO
Error: No mail has been sent. The user should have been subscribed to
"RFQ Approved" to receive an email.

OPW-2447234

closes odoo/odoo#71892

X-original-commit: b459fc86d895dcd0c4bab8bb8332241fe9a43a6f
Signed-off-by: Adrien Widart <adwid@users.noreply.github.com>
Signed-off-by: William Henrotin <Whenrow@users.noreply.github.com>

addons/purchase/models/purchase.py

@@ -252,7 +252,9 @@ class PurchaseOrder(models.Model):
     def _track_subtype(self, init_values):
         self.ensure_one()
         if 'state' in init_values and self.state == 'purchase':
-            return self.env.ref('purchase.mt_rfq_approved')
+            if init_values['state'] == 'to approve':
+                return self.env.ref('purchase.mt_rfq_approved')
+            return self.env.ref('purchase.mt_rfq_confirmed')
         elif 'state' in init_values and self.state == 'to approve':
             return self.env.ref('purchase.mt_rfq_confirmed')
         elif 'state' in init_values and self.state == 'done':