A workaround would be to create a SharePoint Item level Transformer to change the Attachments Column metadata from True to False
$dataObject["Attachments"] = $false
Link to instructions on to add a transformer to a migration job are below:
DISCLAIMER
Quest is providing this PowerShell script (hereafter called the "Transformer") available for general use.
The Transformer has not been tested or approved for use in a production environment.
By using the Transformer Customer acknowledges and assumes the risk of installing, using, and relying upon this Transformer.
Any and all modifications to this Transformer made by Quest for specific uses outside of its original intent will require additional Professional Services.