Clear the Shopify tax adjustment before recalculating it

Closes #14143
(grafted from 27d0430555b070fcca637c9a0dab40c083d7db15)

--HG--
branch : 7.0

modules/web_shop_shopify/tests/scenario_web_shop_shopify.rst

@@ -599,7 +599,7 @@ Ignore shipment exception::
     >>> sale.reload()
     >>> invoice, = sale.invoices
     >>> invoice.total_amount
-    Decimal('164.52')
+    Decimal('164.53')
     >>> payment, = sale.payments
     >>> payment.state
     'succeeded'

modules/web_shop_shopify/web.py

@@ -573,6 +573,7 @@ class Shop(metaclass=PoolMeta):
                     sale.untaxed_amount_cache = None
                     sale.tax_amount_cache = None
                     sale.total_amount_cache = None
+                    sale.shopify_tax_adjustment = None
                     to_update[sale] = order
                     states_to_restore[sale.state].append(sale)
         Sale.write(list(to_update.keys()), {'state': 'draft'})
@@ -582,6 +583,7 @@ class Shop(metaclass=PoolMeta):
         for sale, order in to_update.items():
             sale.shopify_tax_adjustment = (
                 Decimal(order.current_total_price) - sale.total_amount)
+        Sale.save(to_update.keys())
         Sale.store_cache(to_update.keys())
         Amendment._clear_sale(to_update.keys())
         to_process, to_quote = [], []