[FIX] stock: add mising depends on computed field

The field had no triggers on the compute method.
As the field is not stored, it works fine in most cases where the value is
computed in a different transaction that the modification but when it is the
case (e.g. OCA/connector-prestashop#101), the values were incorrect

Add the correct triggers to recompute the value when needed

closes odoo/odoo#30024

Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>

addons/stock/models/product.py

@@ -444,6 +444,10 @@ class ProductTemplate(models.Model):
         relation="stock.location.route", string="Category Routes",
         related='categ_id.total_route_ids')
 
+    @api.depends(
+        'product_variant_ids',
+        'product_variant_ids.stock_quant_ids',
+    )
     def _compute_quantities(self):
         res = self._compute_quantities_dict()
         for template in self: