solfege: Add gdk-pixbuf dependency.

An error occurs at startup without this change.
It is in nativeBuildInputs instead of buildInputs because
the fix does not work in buildInputs.

pkgs/misc/solfege/default.nix

@@ -1,6 +1,6 @@
 { lib, fetchurl, gettext, pkg-config, texinfo, wrapGAppsHook
 , buildPythonApplication, pycairo, pygobject3
-, gobject-introspection, gtk3, librsvg
+, gdk-pixbuf, gobject-introspection, gtk3, librsvg
 , alsa-utils, timidity, mpg123, vorbis-tools, csound, lilypond
 , automake, autoconf, txt2man
 }:
@@ -29,7 +29,7 @@ buildPythonApplication rec {
   nativeBuildInputs = [
     automake
     autoconf
-
+    gdk-pixbuf
     gettext
     pkg-config
     texinfo