Fix warnings in source-version of the project

Author: kzu

src/CloudStorageAccount/CloudStorageAccount.cs

@@ -1,4 +1,5 @@
 // <auto-generated />
+#nullable enable
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;

src/CloudStorageAccount/StorageCredentials.cs

@@ -1,4 +1,5 @@
 // <auto-generated />
+#nullable enable
 using System;
 using System.ComponentModel;
 using Azure.Core;