Update tox requirement from <4.19,>=4.16.0 to >=4.16.0,<4.21

[dependabot[bot]]

Updates the requirements on tox to permit the latest version.

Changelog

Sourced from tox's changelog.

v4.20.0 (2024-09-18)

Features - 4.20.0

- Separate the list dependencies functionality to a separate abstract class allowing code reuse in plugins (such as
  ``tox-uv``) - by :gaborbernat`. (:issue:`3347`)
v4.19.0 (2024-09-17)
Features - 4.19.0

• Support pypy-<major>.<minor> environment names for PyPy environments - by :user:gaborbernat. (:issue:3346)

v4.18.1 (2024-09-07)

Bugfixes - 4.18.1

- Fix and test the string spec for the ``sys.executable`` interpreter (introduced in :pull:`3325`)
  - by :user:`hroncok` (:issue:`3327`)
Improved Documentation - 4.18.1

• Changes the tox_env_teardown docstring to explain the hook is called after a tox env was teared down. (:issue:3305)

v4.18.0 (2024-08-13)

Features - 4.18.0

- Suppress spinner in parallel runs in CI - by :user:`ziima`. (:issue:`3318`)
Bugfixes - 4.18.0

• Boost temporary directories cleanup in tests - by :user:ziima. (:issue:3278)
• Fix absolute base python paths conflicting - by :user:gaborbernat. (:issue:3325)

v4.17.1 (2024-08-07)

Bugfixes - 4.17.1

- Support for running ``-e <major>.<minor>`` has been lost, fixing it - by :user:`gaborbernat`. (:issue:`2849`)
- ``base_python`` now accepts absolute paths to interpreter executable - by :user:`paveldikov`. (:issue:`3191`)
v4.17.0 (2024-08-05)
</tr></table>

... (truncated)

Commits

• a04cc3a release 4.20.0
• 4d8f5fd Separate list dependencies to a separate installer class (#3347)
• 0cb816c YML to YAML
• 2f83624 release 4.19.0
• ed6b0dc Add pypy-major.minor environment name support (#3346)
• 8127c7f [pre-commit.ci] pre-commit autoupdate (#3345)
• 8cadfa2 [pre-commit.ci] pre-commit autoupdate (#3341)
• df34192 release 4.18.1
• 9c6f835 Add 3.13 to CI and bump deps (#3339)
• 9138e15 Bump pypa/gh-action-pypi-publish from 1.9.0 to 1.10.1 (#3338)
• Additional commits viewable in compare view

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