[FIX] mrp: fixed product inventory uom issue

Before this commit, we are getting error that product_uom must be
matched because when we're adding line to inventory after updating the
quantity, product_uom changes to Units.

After this commit, error will not be generated as the default value of
product_uom_id is removed.

Fixes #29305

closes odoo/odoo#29371

addons/stock/models/stock_inventory.py

@@ -331,8 +331,7 @@ class InventoryLine(models.Model):
         index=True, required=True)
     product_uom_id = fields.Many2one(
         'uom.uom', 'Product Unit of Measure',
-        required=True,
-        default=lambda self: self.env.ref('uom.product_uom_unit', raise_if_not_found=True))
+        required=True)
     product_uom_category_id = fields.Many2one(string='Uom category', related='product_uom_id.category_id', readonly=True)
     product_qty = fields.Float(
         'Checked Quantity',