Add CI job that verifies that THIS code base does not contain any unicode

[faern]

To prevent this tool from being attacked by various under cover unicode attacks, we must protect this code base from the same things that the tool tries to protect others from.

I feel like it would be iffy to rely on a self scan. Then a successful attack on unicop can then hide future attacks on unicop. Instead I think we should simply say that unicop is ASCII only, and use some much simpler way to just check for that. For example with iconv --from-code=ascii --to-code=ascii $file.