Update tracing-opentelemetry requirement from 0.20.0 to 0.21.0 (#44)

Updates the requirements on [tracing-opentelemetry](https://github.com/tokio-rs/tracing-opentelemetry) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/tracing-opentelemetry/releases)
- [Changelog](https://github.com/tokio-rs/tracing-opentelemetry/blob/v0.1.x/CHANGELOG.md)
- [Commits](tokio-rs/tracing-opentelemetry@v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: tracing-opentelemetry
  dependency-type: direct:production
...

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

Cargo.toml

@@ -13,7 +13,7 @@ tracing = { version = "0.1.30", features = ["attributes"] }
 tracing-subscriber = { version = "0.3.8", features = ["env-filter"] }
 opentelemetry = "0.20.0"
 opentelemetry-jaeger = "0.19.0"
-tracing-opentelemetry = "0.20.0"
+tracing-opentelemetry = "0.21.0"
 
 # Tokio to Axum and all that's in between.
 tokio = { version = "1", features = ["full"] }