Update rcgen requirement from 0.11 to 0.12

Updates the requirements on [rcgen](https://github.com/rustls/rcgen) to permit the latest version.
- [Commits](rustls/rcgen@v0.11.0...v0.12.0)

---
updated-dependencies:
- dependency-name: rcgen
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Cargo.toml

@@ -30,7 +30,7 @@ tower-layer = "0.3"
 anyhow = "1"
 axum = { version = "0.6", default-features = false }
 futures-util = { version = "0.3", default-features = false }
-rcgen = { version = "0.11", default-features = false }
+rcgen = { version = "0.12", default-features = false }
 reqwest = { version = "0.11", default-features = false, features = ["rustls-tls-manual-roots"] }
 tokio = { version = "1", features = ["macros", "rt-multi-thread"] }