chore(deps): update pyo3 requirement from 0.19 to 0.20

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@v0.19.0...v0.19.2)

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

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

Cargo.toml

@@ -75,7 +75,7 @@ members = ["pyrs", "compile-rewriter", "taso-optimiser"]
 
 quantinuum-hugr = { git = "https://github.com/CQCL-DEV/hugr", rev = "9254ac7" }
 portgraph = { version = "0.9", features = ["serde"] }
-pyo3 = { version = "0.19" }
+pyo3 = { version = "0.20" }
 itertools = { version = "0.11.0" }
 tket-json-rs = { git = "https://github.com/CQCL/tket-json-rs", rev = "619db15d3", features = [
     "tket2ops",