⬆️ Update pyo3 requirement from 0.20 to 0.21

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...v0.21.2)

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

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

python/extension/Cargo.toml

@@ -21,7 +21,7 @@ rayon = { version = "1.7" }
 rayon-cond = { version = "0.3" }
 anyhow = { version = "1.0" }
 serde = { version = "1.0", features = ["derive"] }
-pyo3 = { version = "0.20", features = ["extension-module", "anyhow", "serde"] }
+pyo3 = { version = "0.21", features = ["extension-module", "anyhow", "serde"] }
 mimalloc = { version = "0.1", default-features = false, optional = true }
 
 [dependencies.ltp]