dev-perl/Gtk2: Require jpeg support in gdk-pixbuf for testing

dev-perl/Gtk2: Require jpeg support in gdk-pixbuf for testing

Tests fail without gdk-pixbuf compiled with jpeg support:

=GdkPixbuf-LOG **: gdk_pixbuf_from_pixdata() called on: at t/GdkPixbuf.t line 185.
GdkPixbuf-LOG **:       Encoding rle at t/GdkPixbuf.t line 185.
GdkPixbuf-LOG **:       Dimensions: 4 x 5 at t/GdkPixbuf.t line 185.
GdkPixbuf-LOG **:       Rowstride: 16, Length: 91 at t/GdkPixbuf.t line 185.
GdkPixbuf-LOG **:       Copy pixels == true at t/GdkPixbuf.t line 185.
Image type 'jpeg' is not supported at t/GdkPixbuf.t line 200.
t/GdkPixbuf.t ...................... Dubious, test returned 255 (wstat 65280, 0xff00)

Package-Manager: Portage-2.3.6, Repoman-2.3.2