Publish Brazilian Portuguese translation (#381)

The IETF language tag for “Brazilian Portuguese” is “pt-BR”[1]. This
tag is also used in the HTML lang attribute[2].

We derive the language code directly from the “.po” filename, so I’ve
renamed “pt_BR.po” to “pt-BR.po” make everything use the correct
language code. Nothing in the Gettext pipeline cares about the precise
filename, so it should be fine to rename it like this.

[1]: https://en.wikipedia.org/wiki/Brazilian_Portuguese#Language_codes
[2]: https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/lang

.github/workflows/publish.yml

@@ -18,7 +18,7 @@ concurrency:
 
 env:
   CARGO_TERM_COLOR: always
-  LANGUAGES: da
+  LANGUAGES: da pt-BR
 
 jobs:
   publish: