Missing interrupt handler 0x21, operation=0x67

[gregoral]

When I try to execute an executable I immediately get an exception.

Spice86.Core.Emulator.InterruptHandlers.UnhandledInterruptException
Error is: callbackNumber=0x21, operation=0x67

To Reproduce
It will be hard to reproduce without an executable that tries to call this specific interrupt.

Expected behavior
Spice86 should be able to handle this interrupt.

Desktop (please complete the following information):

• OS: Windows
• Version 11

Additional context
This is the code from DOSBox that handles this interrupt:

case 0x67:                    /* Set handle count */
/* Weird call to increase amount of file handles needs to allocate memory if >20 */
{
    DOS_PSP psp(dos.psp());
    psp.SetNumFiles(reg_bx);
    CALLBACK_SCF(false);
    break;
};

I'm willing to create a fix.
As discussed on discord, I will fork the repo and prepare a PR with a fix for the issue.