Add test case using empty line (#473)

See <https://gitlab.haskell.org/ghc/ghc/-/issues/23984>

Author: jaspervdj

tests/Language/Haskell/Stylish/Step/LanguagePragmas/Tests.hs

@@ -230,7 +230,7 @@ case13 = assertSnippet
     input =
         [ "{-# LANGUAGE BangPatterns  #-}"
         , "{-# LANGUAGE DeriveFunctor #-}"
-        , "module Main where"
+        , ""
         , "main = let !x = 1 + 1 in print x"
         ]