chore(deps): update pyo3 requirement from 0.20 to 0.21

[dependabot]

Updates the requirements on pyo3 to permit the latest version.

Release notes

Sourced from pyo3's releases.

PyO3 0.20.3

This is a stability & compatibility release to fix a couple of minor compilation edge cases from PyO3 0.20.2.

The portable-atomic dependency has been added to resolve compile failures on platforms without 64-bit atomic support.

A maximum Python version check (currently for Python 3.12) has been added to prevent using old PyO3 code against future Python versions beyond the supported range.

Thank you to the following users for the improvements:

@​adamreichold @​davidhewitt

Changelog

Sourced from pyo3's changelog.

[0.20.3] - 2024-02-23

Packaging

• Add portable-atomic dependency. #3619
• Check maximum version of Python at build time and for versions not yet supported require opt-in to the abi3 stable ABI by the environment variable PYO3_USE_ABI3_FORWARD_COMPATIBILITY=1. #3821

Fixed

• Use portable-atomic to support platforms without 64-bit atomics. #3619
• Fix compilation failure with either feature enabled without experimental-inspect enabled. #3834

[0.20.2] - 2024-01-04

Packaging

• Pin pyo3 and pyo3-ffi dependencies on pyo3-build-config to require the same patch version, i.e. pyo3 0.20.2 requires exactly pyo3-build-config 0.20.2. #3721

Fixed

• Fix compile failure when building pyo3 0.20.0 with latest pyo3-build-config 0.20.X. #3724
• Fix docs.rs build. #3722

[0.20.1] - 2023-12-30

Added

• Add optional either feature to add conversions for either::Either<L, R> sum type. #3456
• Add optional smallvec feature to add conversions for smallvec::SmallVec. #3507
• Add take and into_inner methods to GILOnceCell #3556
• #[classmethod] methods can now also receive Py<PyType> as their first argument. #3587
• #[pyfunction(pass_module)] can now also receive Py<PyModule> as their first argument. #3587
• Add traverse method to GILProtected. #3616
• Added abi3-py312 feature #3687

Fixed

• Fix minimum version specification for optional chrono dependency. #3512
• Silenced new clippy::unnecessary_fallible_conversions warning when using a Py<Self> self receiver. #3564

[0.20.0] - 2023-10-11

Packaging

• Dual-license PyO3 under either the Apache 2.0 OR the MIT license. This makes the project GPLv2 compatible. #3108
• Update MSRV to Rust 1.56. #3208
• Bump indoc dependency to 2.0 and unindent dependency to 0.2. #3237
• Bump syn dependency to 2.0. #3239
• Drop support for debug builds of Python 3.7. #3387

... (truncated)

Commits

• 901f54b release: 0.20.3
• 2329862 ci: workaround more aggressive nightly rust lints
• 284d6ee ci: updates for Rust 1.76
• 482883a fix either feature conditional compilation, again (#3834)
• c375c8a add maximum Python version check (#3821)
• 9d1b11f Use portable-atomic for targets which lack 64-bit atomics used to check inter...
• 4774ded Merge pull request #3725 from PyO3/release-0.20.2
• bcef18b release: 0.20.2
• fa6d60b Use a definite version specification when depending on pyo3-build-config.
• f9f0bdd Merge pull request #3724 from davidhewitt/fix-build-config-issue
• Additional commits viewable in compare view

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[aborgna-q]

Closing, as 0.21 is a big update that will need manual updating, and requires tket-json-rs to update first.

[dependabot]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version. You can also ignore all major, minor, or patch releases for a dependency by adding an ignore condition with the desired update_types to your config file.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.