test: set schedule date on PO before insert

(cherry picked from commit 5af60cf2e3)

erpnext/stock/doctype/material_request/test_material_request.py

@@ -58,7 +58,9 @@ class TestMaterialRequest(FrappeTestCase):
 		# fully order the first item, leave the second pending
 		po = make_purchase_order(mr.name)
 		po.supplier = "_Test Supplier"
+		po.schedule_date = today()
 		po.items = [po.items[0]]
+		po.items[0].schedule_date = today()
 		po.insert()
 		po.submit()