Fix usage of the glib::flags derive
Fix usage of the glib::flags derive

Individual flags use

  #[flags_value(name="FOO_BAR", nick="foo-bar")]

not

  #[gflags(name="FOO_BAR", nick="foo-bar")]

Shouldn't gtk-rs-core have caught this unknown attribute?

Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/634>

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg