Set-AzDataFactoryV2Pipeline ignores additionalColumns

### Description

Hello, I use Set-AzDataFactoryV2Pipeline for deployment automation.
Some pipelines contain copy activities with JsonSource and additionalColumns.
Manually deploying still works as expected but using Set-AzDataFactoryV2Pipeline and the DefinitionFile parameter, deploys the pipelines without additionalColumns.
It worked in the past, but not longer.
I executed `Update-Module Az.*` before my latest test.

### Issue script & Debug output

```PowerShell
Set-AzDataFactoryV2Pipeline -DefinitionFile MyPipeline.json
```

### Environment data

```PowerShell
Name Value
---- -----
PSVersion 7.5.0
PSEdition Core
GitCommitId 7.5.0
OS Microsoft Windows 10.0.22631
Platform Win32NT
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1
WSManStackVersion 3.0
```

### Module versions

```PowerShell
ModuleType Version PreRelease Name ExportedCommands
---------- ------- ---------- ---- ----------------
Script 2.16.0 Az.Accounts {Add-AzEnvironment, Clear-AzConfig, Clear-AzContext, Clear-AzDefault…}
Script 1.18.3 Az.DataFactory {Add-AzDataFactoryV2DataFlowDebugSessionPackage, Add-AzDataFactoryV2TriggerSubscription, Get-AzDataFactory, Get-AzDataFactoryActivityWindow…}
Script 4.14.0 Az.Sql {Add-AzSqlDatabaseToFailoverGroup, Add-AzSqlElasticJobStep, Add-AzSqlElasticJobTarget, Add-AzSqlInstanceKeyVaultKey…}
```

### Error output

```PowerShell

```

Start with the Set-AzDataFactoryV2Pipeline entry point and its DefinitionFile handling, then reproduce the deployment using the reported PowerShell command and a pipeline containing a JsonSource with additionalColumns. Trace where those fields are lost and verify that the deployed pipeline retains additionalColumns; the issue provides no named files or tests.

Written by the indexing model from the issue text.