Serialization of HashMap containing `Value` as values broken for GVariant format

This code

#[derive(Deserialize, Serialize, Type, PartialEq, Debug)]
struct ZVStruct<'s>(#[serde(borrow)] HashMap<&'s str, Value<'s>>);

let mut dict = HashMap::new();
dict.insert("hi", Value::from("hello"));
dict.insert("bye", Value::from("then"));

let element = ZVStruct(dict);

let ctxt = Context::<LE>::new_gvariant(0);
let signature = ZVStruct::signature();

let encoded = to_bytes_for_signature(ctxt, &signature, &element).unwrap();

fails with panicked at 'calledResult::unwrap()on anErrvalue: Message("invalid type: characters, expected s, g, oorv")' from the serializer. The issue is specific to Dict in a Value. Interestingly we don't get any error if there is only 1 entry in the dict.