[FIX] maintenance: don't copy stage
[FIX] maintenance: don't copy stage

When duplicating maintenance request, the stage should be reset to the
first one (which is +/- what the default does).

Fixes odoo/odoo#38558

closes odoo/odoo#39327

X-original-commit: 14642826601070960fdd79ebd74ebd407e00617c
Signed-off-by: Martin Trigaux (mat) <cc7c5be316e48d137cbb549833b85d91034d799d@odoo.com>

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo