[FIX] sale: group invoices by partner as expected

Steps to reproduce the problem:

- Create 2 partners A and B.
- Create sales orders in this order: Order Partner A + Order Partner B + Order Partner B + Order Partner A + Order Partner B
- Select all that orders.
- Invoice them.

Current behavior: 4 invoices are created.

Expected behavior: Only 2 invoices are created: Invoice Partner A + Invoice Partner B

This is because itertools.groupby expects elements to be pre-sorted by
the grouping key, so we sort them accordingly.

closes odoo/odoo#73559

X-original-commit: 3b0bd35c6c9e54b7b0c21cc28f55f520c884d9ad
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>

addons/sale/models/sale_order.py

@@ -742,6 +742,12 @@ Reason(s) of this behavior could be:
         if not grouped:
             new_invoice_vals_list = []
             invoice_grouping_keys = self._get_invoice_grouping_keys()
+            invoice_vals_list = sorted(
+                invoice_vals_list,
+                key=lambda x: [
+                    x.get(grouping_key) for grouping_key in invoice_grouping_keys
+                ]
+            )
             for grouping_keys, invoices in groupby(invoice_vals_list, key=lambda x: [x.get(grouping_key) for grouping_key in invoice_grouping_keys]):
                 origins = set()
                 payment_refs = set()