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...v0.21.0)

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

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

arrow/Cargo.toml

@@ -54,7 +54,7 @@ arrow-select = { workspace = true }
 arrow-string = { workspace = true }
 
 rand = { version = "0.8", default-features = false, features = ["std", "std_rng"], optional = true }
-pyo3 = { version = "0.20", default-features = false, optional = true }
+pyo3 = { version = "0.21", default-features = false, optional = true }
 
 [package.metadata.docs.rs]
 features = ["prettyprint", "ipc_compression", "ffi", "pyarrow"]