API: Expose cancellation_date on order endpoint (Z#23170733) (#4606)

Co-authored-by: robbi5 <richt@rami.io>

src/tests/api/test_order_create.py

@@ -492,6 +492,7 @@ def test_order_create_simulate(token_client, organizer, event, item, quota, ques
         'refunds': [],
         'require_approval': False,
         'sales_channel': 'web',
+        'cancellation_date': None
     }
 
 

src/tests/api/test_orders.py

@@ -337,6 +337,7 @@ TEST_ORDER_RES = {
     "downloads": [],
     "payments": TEST_PAYMENTS_RES,
     "refunds": TEST_REFUNDS_RES,
+    "cancellation_date": None,
 }