Update rustls requirement from 0.19 to 0.20 in /gremlin-client (#144)

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/OLDCHANGES.md)
- [Commits](rustls/rustls@v/0.19.0...v/0.20.0)

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

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

gremlin-client/Cargo.toml

@@ -51,7 +51,7 @@ async-tls =  { version = "0.11", optional = true }
 tokio-native-tls = { version = "0.3.0", optional = true }
 tokio-stream = { version = "0.1.2", optional = true }
 gremlin-derive = { path="../gremlin-derive", version="0.1", optional=true }
-rustls =   { version="0.19", features = ["dangerous_configuration"], optional = true}
+rustls =   { version="0.20", features = ["dangerous_configuration"], optional = true}
 webpki = { version = "0.21.3", optional = true }
 thiserror = "1.0.20"