2.3.0 breaks `HashMap` serialization as `Vec` of pairs with `bincode`

[stefunctional]

HashMap serialization as Vec of pairs with bincode that worked with serde_with 2.2.0 breaks with 2.3.0.

Reproduction

Cargo.toml:

[package]
name = "playground"
version = "0.1.0"
edition = "2021"

[dependencies]
bincode = "1.3.3"
serde = { version = "1.0.154", features = ["derive"] }
serde_with = "=2.3.0"

src/lib.rs:

use serde::Serialize;
use serde_with::serde_as;
use std::collections::HashMap;

#[serde_as]
#[derive(Debug, Default, Serialize)]
struct Foo {
    #[serde_as(as = "Vec<(_, _)>")]
    xs: HashMap<i32, i32>,
}

fn main() {
    bincode::serialize(&Foo::default()).unwrap();
}

Expected output

cargo run passes with no output.

Actual output

cargo run fails with:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: SequenceMustHaveLength', src/main.rs:13:41

[jonasbb]

Hi, thanks for the bug report. Sorry for the inconvenience. I think that is a side effect of the changes done for #565. There are other issues with that, so it will need to be reverted.

[stephaneyfx]

No worries. Thank you for this useful crate!