CI: Autogen fontfilenames file

[Finii]

The fontfilenames file has been forgotten (but I also hate that the information is scattered so much), probably we should autogenerate that file instead.

https://github.com/ryanoasis/nerd-fonts/tree/master/src/unpatched-fonts#regenerating-the-fontfilenames-file

Originally posted by @Finii in #1895 (review)