Rename pt.po back to pt_BR.po (#11073)

Follow-up to #10976.

Portugal exists! [Wikipedia notes it] to be the main other dialect.
There's already a PR for `pt_PT` support too: #9078.

[Wikipedia notes it]: https://en.wikipedia.org/wiki/Portuguese_dialects

CODEOWNERS

@@ -184,7 +184,7 @@
 /po/nb.po @ghostty-org/nb_NO
 /po/nl.po @ghostty-org/nl_NL
 /po/pl.po @ghostty-org/pl_PL
-/po/pt.po @ghostty-org/pt_BR
+/po/pt_BR.po @ghostty-org/pt_BR
 /po/ru.po @ghostty-org/ru_RU
 /po/tr.po @ghostty-org/tr_TR
 /po/uk.po @ghostty-org/uk_UA

src/os/i18n_locales.zig

@@ -43,7 +43,7 @@ pub const locales = [_][:0]const u8{
     "id",
     "es_BO",
     "es_AR",
-    "pt",
+    "pt_BR",
     "ca",
     "it",
     "bg",