xfce4_windowck_plugin: fix build

pkgs/desktops/xfce/panel-plugins/xfce4-windowck-plugin.nix

···
   buildInputs = [ pkgconfig intltool python3 imagemagick libwnck gtk2
     exo libxfce4ui libxfce4util xfce4panel xfconf xfce4_dev_tools ];
 
-  preConfigure = "./autogen.sh";
+  preConfigure = ''
+    ./autogen.sh
+    patchShebangs .
+  '';
 
   enableParallelBuilding = true;