There's a merged pull request on the void-packages repository

tox: update to 3.28.0, orphan.
https://github.com/void-linux/void-packages/pull/42299

Description:
<!-- Uncomment relevant sections and delete options which are not applicable -->

#### Testing the changes
- I tested the changes in this PR: **briefly**

Tox was packaged for do_check, but it runs in virtualenv, thus not useful.
Maybe it could be made work with [sitepackages](https://tox.wiki/en/latest/config.html#sitepackages).

<!--
#### New package
- This new package conforms to the [package requirements](https://github.com/void-linux/void-packages/blob/master/CONTRIBUTING.md#package-requirements): **YES**|**NO**
-->

<!-- Note: If the build is likely to take more than 2 hours, please add ci skip tag as described in
https://github.com/void-linux/void-packages/blob/master/CONTRIBUTING.md#continuous-integration
and test at least one native build and, if supported, at least one cross build.
Ignore this section if this PR is not skipping CI.
-->
<!--
#### Local build testing
- I built this PR locally for my native architecture, (ARCH-LIBC)
- I built this PR locally for these architectures (if supported. mark crossbuilds):
  - aarch64-musl
  - armv7l
  - armv6l-musl
-->