cargo(deps): update axum-extra requirement in /rustmail

Updates the requirements on [axum-extra](https://github.com/tokio-rs/axum) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/axum/releases)
- [Changelog](https://github.com/tokio-rs/axum/blob/main/CHANGELOG.md)
- [Commits](tokio-rs/axum@axum-extra-v0.10.3...axum-extra-v0.12.2)

---
updated-dependencies:
- dependency-name: axum-extra
  dependency-version: 0.12.2
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

rustmail/Cargo.toml

@@ -16,7 +16,7 @@ async-trait = "0.1.89"
 chrono = { version = "0.4.42", features = ["serde"] }
 regex = "1.11.3"
 axum = "0.8.6"
-axum-extra = { version = "0.10.3", features = ["cookie"] }
+axum-extra = { version = "0.12.2", features = ["cookie"] }
 hyper = "1.7.0"
 rust-embed = "8.7.2"
 mime_guess = "2.0.5"