chore(deps): update dependency tox to v4.29.0 (#843)

This PR contains the following updates:

| Package | Change | Age | Confidence |
|---|---|---|---|
| [tox](https://redirect.github.com/tox-dev/tox)
([changelog](https://tox.wiki/en/latest/changelog.html)) | `==4.28.4` ->
`==4.29.0` |
[![age](https://developer.mend.io/api/mc/badges/age/pypi/tox/4.29.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/tox/4.28.4/4.29.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>tox-dev/tox (tox)</summary>

###
[`v4.29.0`](https://redirect.github.com/tox-dev/tox/releases/tag/4.29.0)

[Compare
Source](https://redirect.github.com/tox-dev/tox/compare/4.28.4...4.29.0)

<!-- Release notes generated using configuration in .github/release.yml
at 4.29.0 -->

#### What's Changed

- Docs: environment variables contain strings by
[@&#8203;hroncok](https://redirect.github.com/hroncok) in
[#&#8203;3575](https://redirect.github.com/tox-dev/tox/pull/3575)
- 🐍 Fix sys\_platform Fixture Leakage breaking the CI by
[@&#8203;gaborbernat](https://redirect.github.com/gaborbernat) in
[#&#8203;3589](https://redirect.github.com/tox-dev/tox/pull/3589)
- Expose a new `tox_extend_envs` hook in plugins API by
[@&#8203;webknjaz](https://redirect.github.com/webknjaz) in
[#&#8203;3591](https://redirect.github.com/tox-dev/tox/pull/3591)

**Full Changelog**:
<tox-dev/tox@4.28.4...4.29.0>

</details>

---

### Configuration

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♻ **Rebasing**: Whenever PR is behind base branch, or you tick the
rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

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requirements-dev.txt

@@ -1,6 +1,6 @@
 -r requirements.txt
 -r requirements-test.txt
-tox==4.28.4
+tox==4.29.0
 wheel==0.46.1
 Sphinx==7.4.7
 sphinx-rtd-theme==3.0.2