rust: Enable GNOME 46

[sonnyp]

Unfortunately running a Rust project fails with

   Compiling gtk4 v0.8.1
error[E0425]: cannot find function `gtk_popover_menu_new_from_model_full` in crate `ffi`
     --> /home/sonny/.cargo/registry/src/index.crates.io-6f17d22bba15001f/gtk4-0.8.1/src/auto/popover_menu.rs:46:41
      |
46    |             Widget::from_glib_none(ffi::gtk_popover_menu_new_from_model_full(
      |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: a function with a similar name exists: `gtk_popover_menu_new_from_model`
      |
     ::: /home/sonny/.cargo/registry/src/index.crates.io-6f17d22bba15001f/gtk4-sys-0.8.0/src/lib.rs:16066:5
      |
16066 |     pub fn gtk_popover_menu_new_from_model(model: *mut gio::GMenuModel) -> *mut GtkWidget;
      |     ------------------------------------------------------------------------------------- similarly named function `gtk_popover_menu_new_from_model` defined here

error[E0425]: cannot find function `gtk_popover_menu_flags_get_type` in crate `ffi`
     --> /home/sonny/.cargo/registry/src/index.crates.io-6f17d22bba15001f/gtk4-0.8.1/src/auto/flags.rs:1101:33
      |
1101  |         unsafe { from_glib(ffi::gtk_popover_menu_flags_get_type()) }
      |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: a function with a similar name exists: `gtk_popover_menu_bar_get_type`
      |
     ::: /home/sonny/.cargo/registry/src/index.crates.io-6f17d22bba15001f/gtk4-sys-0.8.0/src/lib.rs:16097:5
      |
16097 |     pub fn gtk_popover_menu_bar_get_type() -> GType;
      |     ----------------------------------------------- similarly named function `gtk_popover_menu_bar_get_type` defined here

    Building [=======================> ] 227/233: gtk4