[FIX] product: hide cost label from the view if product with variant

The group `“base.group_user”` is added in the view for the field
`standard_price` while it is already set on the python side:
https://github.com/odoo/odoo/blob/16.0/addons/product/models/product_template.py#L76


this causes an issue in the case of a product with variants,
the invisible attrs is ignored, the `standard_price` and
`uom_name` field are hidden, but the label will still be displayed

opw-3076827

closes odoo/odoo#106842

Signed-off-by: William Henrotin (whe) <whe@odoo.com>