Because Electron Fiddles seem to be moved to temporary directories before execution, and the icon files seem not to be moved - it seems like there's no way to use an icon file in Electron Fiddle.
Unfortunately I'm not able to browse inside the temporary folder it uses. It uses a path like: C:\Users\Myself\AppData\Local\Temp\tmp-5140Y2pLIyecwgqw\
Is it accurate to think it's not possible, or is there some workaround?