[PM-2943] Enable Nullable Repositories in Unowned Files (#4549)

* Enable Nullable In Unowned Repos

* Update More Tests

* Move to One If

* Fix Collections

* Format

* Add Migrations

* Move Pragma Annotation

* Add Better Assert Message

src/Core/Repositories/IMaintenanceRepository.cs

@@ -1,5 +1,7 @@
 namespace Bit.Core.Repositories;
 
+#nullable enable
+
 public interface IMaintenanceRepository
 {
     Task UpdateStatisticsAsync();