LaTeX reader: Fix regression in package options including underscore.

Closes #4424.

src/Text/Pandoc/Readers/LaTeX.hs

@@ -1162,7 +1162,7 @@ singleChar = try $ do
      else return $ Tok pos toktype t
 
 opt :: PandocMonad m => LP m Inlines
-opt = bracketed inline
+opt = bracketed inline <|> (str . T.unpack <$> rawopt)
 
 rawopt :: PandocMonad m => LP m Text
 rawopt = do

test/command/4424.md

@@ -0,0 +1,10 @@
+```
+% pandoc -f latex -t native
+\documentclass{article}
+\usepackage[sortlocale=en_GB]{biblatex}
+\begin{document}
+Test
+\end{document}
+^D
+[Para [Str "Test"]]
+```