The job service web interface is based on HTTP.sys. The .NET framework does not allow to adjust the behaviour of the "Server" header.
It is possible to disable the server header with a registry entry. Open HKLM\System\CurrentControlSet\Services\HTTP\Parameters and add a DWORD with the name DisableServerHeader and a value of 2. Restart the machine.
For more information, check this article at Microsoft Support's website: https://support.microsoft.com/en-us/help/820129/http-sys-registry-settings-for-windows .
One Identity Support does not provide support for problems that arise from improper modification of the registry. The Windows registry contains information critical to your computer and applications. Make sure you back up the registry before modifying it. For more information on the Windows Registry Editor and how to back up and restore it, refer to Microsoft Article ID 256986 “Description of the Microsoft Windows registry” at Microsoft Support.