fix typo in external font test

FelixPe · andrewtimberlake · commit 3947cc825e1e · 2025-04-25T08:27:46.000+02:00
diff --git a/test/pdf/external_font_test.exs b/test/pdf/external_font_test.exs
@@ -1,5 +1,5 @@
 defmodule Pdf.ExternalFontTest do
-  use ExUnit.Case, asyn: true
+  use ExUnit.Case, async: true
 
   alias Pdf.ExternalFont
   alias Pdf.Font
