Adjust namespaces in the Cache folder

I made these Umbraco.Cms.Core even though they have to reside in infrastructure.

src/Umbraco.Web.BackOffice/Controllers/PublishedSnapshotCacheStatusController.cs

@@ -4,7 +4,7 @@ using Microsoft.AspNetCore.Mvc;
 using Umbraco.Cms.Core.Cache;
 using Umbraco.Cms.Core.PublishedCache;
 using Umbraco.Cms.Web.Common.Attributes;
-using Umbraco.Web.Cache;
+using Umbraco.Extensions;
 using Constants = Umbraco.Cms.Core.Constants;
 
 namespace Umbraco.Cms.Web.BackOffice.Controllers