Correct column nullability in 10.0 what's new page (#5250)

See #5247

Author: roji

entity-framework/core/what-is-new/ef-core-10.0/whatsnew.md

@@ -304,7 +304,7 @@ CREATE TABLE [Customers] (
     [Id] int NOT NULL IDENTITY,
     [Name] nvarchar(max) NOT NULL,
     [ShippingAddress] json NOT NULL,
-    [BillingAddress] json NOT NULL,
+    [BillingAddress] json NULL,
     CONSTRAINT [PK_Customers] PRIMARY KEY ([Id])
 );
 ```