[FIX] mrp: stock.move with reference new

Usecase to reproduce:
- Create a MO as draft
- The stock move inside don't have a reference despite the MO name is
already set.

It happens because the reference and the group are set during the
action_confirm. However it's not great if the user takes time before
confirmation or if he cancels the MO. In those case the reference
on the moves remains 'new'.

opw-2201986

closes odoo/odoo#48568

X-original-commit: 1b7e304a907d8a43d5f561226028a4b353902fab
Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>