chore(deps): update pytest-subtests requirement

Updates the requirements on [pytest-subtests](https://github.com/pytest-dev/pytest-subtests) to permit the latest version.
- [Release notes](https://github.com/pytest-dev/pytest-subtests/releases)
- [Changelog](https://github.com/pytest-dev/pytest-subtests/blob/main/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest-subtests/compare/v0.14.1...v0.15.0)

---
updated-dependencies:
- dependency-name: pytest-subtests
  dependency-version: 0.15.0
  dependency-type: direct:production
...

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