0.38 does not comply to a declared MSRV

[andy128k]

1.56 is declared as a MSRV in Cargo.toml but actually 1.83 is required.

  │ error[E0658]: referencing statics in constant functions is unstable                                                                               │
  │   --> /home/andy/.cargo/registry/src/index.crates.io-6f17d22bba15001f/quick-xml-0.38.3/src/encoding.rs:87:23                                      │
  │    |                                                                                                                                              │
  │ 87 |             encoding: UTF_8,                                                                                                                 │
  │    |                       ^^^^^                                                                                                                  │
  │    |                                                                                                                                              │
  │    = note: see issue #119618 <https://github.com/rust-lang/rust/issues/119618> for more information                                               │
  │    = note: `static` and `const` variables can refer to other `const` variables. A `const` variable, however, cannot refer to a `static` variable. │
  │    = help: to fix this, the value can be extracted to a `const` and then used.       

Allow creating references to statics in const initializers.
https://releases.rs/docs/1.83.0/

[Mingun]

MSRV does not mean that crate should successfully compile with every possible feature set. When no features is enabled, it compiles successfully on 1.56.