Add extra conditional for failover groups going from multi to single secondary (Azure#23613)

* add conditional to persist changes to account for multi -> single scenario

* add changelog update

Author: alecbain

src/Sql/Sql/ChangeLog.md

@@ -21,6 +21,7 @@
 
 ## Version 4.12.0
 * Added new parameters `MaintenanceConfigurationId`, `DnsZone` to `AzSqlInstancePool` cmdlets
+* Fixed `Set-AzSqlDatabaseFailoverGroup` when going from multi-secondary to single secondary
 
 ## Version 4.11.0
 * Added new parameters to `New-AzSqlDatabaseFailoverGroup`, `Set-AzSqlDatabaseFailoverGroup`

src/Sql/Sql/Failover Group/Cmdlet/SetAzureSqlFailoverGroup.cs

@@ -172,7 +172,7 @@ protected override IEnumerable<AzureSqlFailoverGroupModel> ApplyUserInputToModel
         protected override IEnumerable<AzureSqlFailoverGroupModel> PersistChanges(IEnumerable<AzureSqlFailoverGroupModel> entity)
         {
             AzureSqlFailoverGroupModel model = entity.First();
-            bool useV2 = (model.PartnerServers != null && model.PartnerServers.Count > 1);
+            bool useV2 = (model.PartnerServers != null && model.PartnerServers.Count > 1) || (MyInvocation.BoundParameters.ContainsKey("PartnerServerList"));
             return new List<AzureSqlFailoverGroupModel>() {
                 ModelAdapter.PatchUpdateFailoverGroup(entity.First(), useV2)
             };