oldtests: skip Test_spellinfo()

nvim supports only `set encoding=utf8`.

src/nvim/testdir/test_spell.vim

@@ -86,6 +86,7 @@ func Test_spellreall()
 endfunc
 
 func Test_spellinfo()
+  throw 'skipped: Nvim does not support enc=latin1'
   new
 
   set enc=latin1 spell spelllang=en