Fix TODO for flattened_maybe bby using a `literal` macro matcher
/// ```
#[macro_export]
macro_rules! flattened_maybe {
- // TODO Change $field to literal, once the compiler version is bumped enough.
- ($fn:ident, $field:expr) => {
+ ($fn:ident, $field:literal) => {
fn $fn<'de, T, D>(deserializer: D) -> ::std::result::Result<T, D::Error>
where
T: serde_with::serde::Deserialize<'de>,
