Salut Guix!

Since the same string is used to generate both the package names and
source URLs of Aspell dictionaries, dictionaries pt-pt and pt-br have
been producing invalid URLs. Their upstream names are pt_PT and pt_BR.

This could be fixed by changing either the way package names or URLs are
generated. Rather than adapting URLs to special cases, it seems more
straightforward to let the dict-name string represent upstream name, and
then downcase and replace underscores to produce a package name in
accordance with the naming conventions.

This was the simplest/easiest thing I could come up with. Do let me know
if there is a smarter way!

Kind regards,
Jens M