Work around infrequent crash when pen enters proximity on Windows

[Susko3]

• Fixes osu.Framework.Platform.SDL3.SDL3Exception: Invalid pen instance ID (at SDL_GetPenDeviceType(evtPenProximity.which)) #6747

This hard-codes the pen type on Windows to TabletPenDeviceType.Unknown. There is no change in functionality as SDL already reports all pens on Windows as SDL_PEN_DEVICE_TYPE_UNKNOWN.

The crash is fixed by not calling SDL_GetPenDeviceType(), which may sometimes error out with "Invalid pen instance ID".

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I also considered storing the last pen type and using that in the error case, but I found it too hacky, it doesn't fix the underlying issue and increases complexity.

[bdach]

Claim that on Windows SDL_PEN_DEVICE_TYPE_UNKNOWN is always returned appears to check out against my sample size of one (1) osu!-branded XP-Pen Deco Fun XS.

Of particular note I could not even get SDL_EVENT_PEN_PROXIMITY_{IN,OUT} to trigger until XP-Pen drivers were present. So possibly this is due to errant drivers. We will likely never know.