Bump darling from 0.20.8 to 0.20.9 in /lang/rust (#2908)

Bumps [darling](https://github.com/TedDriggs/darling) from 0.20.8 to 0.20.9.
- [Release notes](https://github.com/TedDriggs/darling/releases)
- [Changelog](https://github.com/TedDriggs/darling/blob/master/CHANGELOG.md)
- [Commits](https://github.com/TedDriggs/darling/commits)

---
updated-dependencies:
- dependency-name: darling
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

lang/rust/avro_derive/Cargo.toml

@@ -33,7 +33,7 @@ readme = "README.md"
 proc-macro = true
 
 [dependencies]
-darling = { default-features = false, version = "0.20.8" }
+darling = { default-features = false, version = "0.20.9" }
 proc-macro2 = { default-features = false, version = "1.0.82" }
 quote = { default-features = false, version = "1.0.36" }
 serde_json = { workspace = true }