Bump tox from 3.14.6 to 3.15.0 (#1195)

Bumps [tox](https://github.com/tox-dev/tox) from 3.14.6 to 3.15.0.
- [Release notes](https://github.com/tox-dev/tox/releases)
- [Changelog](https://github.com/tox-dev/tox/blob/master/docs/changelog.rst)
- [Commits](tox-dev/tox@3.14.6...3.15.0)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

requirements-dev.txt

@@ -8,4 +8,4 @@ pytest-json==0.4.0
 pytest-pythonpath==0.7.3
 pylama==7.7.1
 mock==4.0.2
-tox==3.14.6
+tox==3.15.0