Update rustls requirement from 0.20.0 to 0.21.0

Updates the requirements on [rustls](https://github.com/rustls/rustls) to permit the latest version.
- [Release notes](https://github.com/rustls/rustls/releases)
- [Changelog](https://github.com/rustls/rustls/blob/main/RELEASE_NOTES.md)
- [Commits](https://github.com/rustls/rustls/compare/v/0.20.0...v/0.21.0)

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

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

Cargo.toml

@@ -46,7 +46,7 @@ version = "0.2.3"
 
 [dependencies.rustls]
 optional = true
-version = "0.20.0"
+version = "0.21.0"
 
 [dependencies.rustls-native-certs]
 optional = true