Cannot cast gio.Filer properly

[diamondburned]

Functions like (*gtk.FileChooser).File() gio.Filer cannot be casted properly.
It seems like the instance type is not found in the registry, so that should be
investigated upon.

panic: interface conversion: *glib.Object is not gio.Filer: missing method AppendTo [recovered]
	panic: closure error: unexpected panic caught: interface conversion: *glib.Object is not gio.Filer: missing method AppendTo

Closure added at:
	github.com/diamondburned/gotktrix/internal/app/messageview/compose.uploader at /home/diamond/Scripts/gotk4/gotktrix/internal/app/messageview/compose/composer.go:83
	github.com/diamondburned/gotktrix/internal/app/messageview/compose.New.func1 at /home/diamond/Scripts/gotk4/gotktrix/internal/app/messageview/compose/composer.go:53
	github.com/diamondburned/gotk4/pkg/core/glib.goMarshal at /home/diamond/.go/pkg/mod/github.com/diamondburned/gotk4/pkg@v0.0.0-20210820075903-8cbc5d9033e7/core/glib/glib.go:162

goroutine 1 [running]:
github.com/diamondburned/gotk4/pkg/core/closure.(*FuncStack).Panicf(0xc000210ab0, {0x1bae5e4, 0x1b}, {0xc0073d1038, 0x1, 0x1})
	/home/diamond/.go/pkg/mod/github.com/diamondburned/gotk4/pkg@v0.0.0-20210820075903-8cbc5d9033e7/core/closure/funcstack.go:93 +0x8fe
github.com/diamondburned/gotk4/pkg/core/closure.(*FuncStack).TryRepanic(0x0)
	/home/diamond/.go/pkg/mod/github.com/diamondburned/gotk4/pkg@v0.0.0-20210820075903-8cbc5d9033e7/core/closure/funcstack.go:111 +0xc7
panic({0x1975160, 0xc00861c0f0})
	/nix/store/qyakjxlzyzvgns61gm9d7qgyq05jmzgp-go-1.17/share/go/src/runtime/panic.go:1038 +0x215
github.com/diamondburned/gotk4/pkg/gtk/v4.(*FileChooser).File(0xc006742368)
	/home/diamond/.go/pkg/mod/github.com/diamondburned/gotk4/pkg@v0.0.0-20210820075903-8cbc5d9033e7/gtk/v4/gtkfilechooser.go:451 +0xa7

[diamondburned]

Fixed in 5622f54.