0.20.4

Fina Wilke:
      glib-macros: Remove &mut to static mut in object_subclass

Sebastian Dröge:
      Update gir
      Regenerate with latest gir
      Update Cargo.lock
      Update versions to 0.20.4

Tomoaki Kawada:
      glib: Make `<Variant as HasParamSpec>::BuilderFn` generic over lifetimes

eri:
      generate gir without link attribute