Docs not embedded for traits anymore

[Evgenii Pashkin]

Ex. for gio cargo build --features "embed-lgpl-docs" in file auto/settings_backend.rs functions in pub trait SettingsBackendExt: 'static not updated despite docs present.

<!-- trait SettingsBackendExt::fn path_writable_changed -->
Signals that the writability of all keys below a given path may have
changed.

[Guillaume Gomez]

Arf, not good...

[Evgenii Pashkin]

Current version https://gtk-rs.org/docs/gio/trait.SocketListenerExt.html also don't contains docs, so problem was at minimum on previous release

[Evgenii Pashkin]

For gtk comments not generated for these traits PadControllerExtManual, TreeSortableExtManual, EditableSignals etc., config in gtk-rs/gtk#832