desktop: Update egui to v0.28.0

[torokati44]

Changelog: https://github.com/emilk/egui/releases/tag/0.28.0
Fortunately, we have already accommodated for all the API changes in #16704.

[torokati44]

Nightly failure:

error: reached the type-length limit while instantiating `cookie_factory::sequence::tuple::<Vec<u8>, ({closure@cookie_factory::bytes::be_u8<Vec<...>>::{closure#0}}, ..., ...)>`
   --> /home/runner/.cargo/git/checkouts/rust-flash-lso-7db697fbf6bd96f3/2f77055/flash-lso/src/amf3/write.rs:487:21
    |
487 |               let x = tuple((
    |  _____________________^
488 | |                 self.write_type_marker(TypeMarker::Object),
489 | |                 cond(had_object.is_reference(), move |out| {
490 | |                     self.write_object_reference(had_object.as_position().unwrap() as u32)(out)
...   |
508 | |                 ),
509 | |             ))(out);
    | |______________^
    |
    = help: consider adding a `#![type_length_limit="47301832"]` attribute to your crate
    = note: the full type name has been written to '/home/runner/work/ruffle/ruffle/target/ci/deps/flash_lso-4a9cf3934fb8b13e.long-type.txt'

error: could not compile `flash-lso` (lib) due to 1 previous error

😳