ci: bump tox from 4.27.0 to 4.28.0 in /.github/workflows in the ci group

Bumps the ci group in /.github/workflows with 1 update: [tox](https://github.com/tox-dev/tox).


Updates `tox` from 4.27.0 to 4.28.0
- [Release notes](https://github.com/tox-dev/tox/releases)
- [Changelog](https://github.com/tox-dev/tox/blob/main/docs/changelog.rst)
- [Commits](tox-dev/tox@4.27.0...4.28.0)

---
updated-dependencies:
- dependency-name: tox
  dependency-version: 4.28.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: ci
...

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

Author: dependabot[bot]

.github/workflows/constraints.txt

@@ -1 +1 @@
-tox==4.27.0
+tox==4.28.0