chore(deps): update pyo3 requirement from 0.20.0 to 0.21.0

Updates the requirements on [pyo3](https://github.com/pyo3/pyo3) to permit the latest version.
- [Release notes](https://github.com/pyo3/pyo3/releases)
- [Changelog](https://github.com/PyO3/pyo3/blob/main/CHANGELOG.md)
- [Commits](PyO3/pyo3@v0.20.0...v0.20.3)

---
updated-dependencies:
- dependency-name: pyo3
  dependency-type: direct:production
...

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

Cargo.toml

@@ -20,7 +20,7 @@ name = "tket_json_rs"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 uuid = { version = "1.4", features = ["serde"] }
-pyo3 = { version = "0.20.0", optional = true }
+pyo3 = { version = "0.21.0", optional = true }
 pythonize = { version = "0.20.0", optional = true }