Call SaveChanges after creating a new tenant.

Resolve #3618

modules/tenant-management/src/Volo.Abp.TenantManagement.Application/Volo/Abp/TenantManagement/TenantAppService.cs

@@ -56,6 +56,8 @@ namespace Volo.Abp.TenantManagement
 
             await TenantRepository.InsertAsync(tenant);
 
+            await CurrentUnitOfWork.SaveChangesAsync();
+
             using (CurrentTenant.Change(tenant.Id, tenant.Name))
             {
                 //TODO: Handle database creation?