* support negative serials in certificate parsing

but raise a warning every time we see it. also proactively raise on
initial parse of the certificate, not just when accessing the
serial_number attribute

* cargo fmt

* review feedback and changelog

* pssh

* Update CHANGELOG.rst

Co-authored-by: Alex Gaynor <alex.gaynor@gmail.com>

Co-authored-by: Alex Gaynor <alex.gaynor@gmail.com>

This is an awful hybrid, but hopefully puts us on a path to removing this nonsense

Bumps [pyo3](https://github.com/pyo3/pyo3) from 0.15.0 to 0.15.1.
- [Release notes](https://github.com/pyo3/pyo3/releases)
- [Changelog](https://github.com/PyO3/pyo3/blob/main/CHANGELOG.md)
- [Commits](https://github.com/pyo3/pyo3/compare/v0.15.0...v0.15.1)

---
updated-dependencies:
- dependency-name: pyo3
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Bumps [asn1](https://github.com/alex/rust-asn1) from 0.8.6 to 0.8.7.
- [Release notes](https://github.com/alex/rust-asn1/releases)
- [Commits](https://github.com/alex/rust-asn1/compare/0.8.6...0.8.7)

---
updated-dependencies:
- dependency-name: asn1
  dependency-type: direct:production
  update-type: version-update:semver-patch
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these don't make sense for forks so let's not run them

Bumps [actions/setup-python](https://github.com/actions/setup-python) from 2.2.2 to 2.3.0.
- [Release notes](https://github.com/actions/setup-python/releases)
- [Commits](https://github.com/actions/setup-python/compare/v2.2.2...v2.3.0)

---
updated-dependencies:
- dependency-name: actions/setup-python
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

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