[FIX] sale_coupon: add missing dependencies on computed fields

Thanks to @rco-odoo

models/sale_coupon_program.py

@@ -44,6 +44,7 @@ class SaleCouponProgram(models.Model):
     coupon_ids = fields.One2many('sale.coupon', 'program_id', string="Generated Coupons", copy=False)
     coupon_count = fields.Integer(compute='_compute_coupon_count')
     order_count = fields.Integer(compute='_compute_order_count')
+    order_line_ids = fields.Many2many('sale.order.line', store=False, search='_search_order_line_ids')
     company_id = fields.Many2one('res.company', string="Company", default=lambda self: self.env.user.company_id)
     currency_id = fields.Many2one(string="Currency", related='company_id.currency_id', readonly=True)
     validity_duration = fields.Integer(default=1,
@@ -53,12 +54,18 @@ class SaleCouponProgram(models.Model):
         ('unique_promo_code', 'unique(promo_code)', 'The program code must be unique!'),
     ]
 
+    def _search_order_line_ids(self, operator, arg):
+        # just a hack to enable the invalidation of 'order_count'
+        return []
+
+    @api.depends('order_line_ids.product_id')
     def _compute_order_count(self):
         product_data = self.env['sale.order.line'].read_group([('product_id', 'in', self.mapped('discount_line_product_id').ids)], ['product_id'], ['product_id'])
         mapped_data = dict([(m['product_id'][0], m['product_id_count']) for m in product_data])
         for program in self:
             program.order_count = mapped_data.get(program.discount_line_product_id.id, 0)
 
+    @api.depends('coupon_ids')
     def _compute_coupon_count(self):
         coupon_data = self.env['sale.coupon'].read_group([('program_id', 'in', self.ids)], ['program_id'], ['program_id'])
         mapped_data = dict([(m['program_id'][0], m['program_id_count']) for m in coupon_data])