Fix warning with -Z minimal-versions

```
error: non-local `impl` definition, they should be avoided as they go against expectation
   --> src/gen/ast_struct.rs:9:10
    |
  9 | #[derive(Serialize, Deserialize)]
    |          ^^^^^^^^^
    |
    = help: move this `impl` block outside the of the current constant `_IMPL_SERIALIZE_FOR_Abi`
    = note: an `impl` definition is non-local if it is nested inside an item and neither the type nor the trait are at the same nesting level as the `impl` block
    = note: one exception to the rule are anon-const (`const _: () = { ... }`) at top-level module and anon-const at the same nesting as the trait or type
    = note: this lint may become deny-by-default in the edition 2024 and higher, see the tracking issue <rust-lang/rust#120363>
    = note: the derive macro `Serialize` may come from an old version of the `serde_derive` crate, try updating your dependency with `cargo update -p serde_derive`
    = note: `-D non-local-definitions` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(non_local_definitions)]`
    = note: this error originates in the derive macro `Serialize` (in Nightly builds, run with -Z macro-backtrace for more info)
```

Cargo.toml

@@ -33,8 +33,8 @@ json = ["serde_json"]
 # Note: proc-macro2, serde, serde_json, and syn are public dependencies.
 [dependencies]
 proc-macro2 = { version = "1.0.60", default-features = false }
-serde = "1.0.103"
-serde_derive = "1.0.103"
+serde = "1.0.165"
+serde_derive = "1.0.165"
 syn = { version = "2", default-features = false, features = ["full"] }
 
 serde_json = { version = "1", optional = true }