Bump marshmallow from 3.5.2 to 3.6.0

Bumps [marshmallow](https://github.com/marshmallow-code/marshmallow) from 3.5.2 to 3.6.0.
- [Release notes](https://github.com/marshmallow-code/marshmallow/releases)
- [Changelog](https://github.com/marshmallow-code/marshmallow/blob/dev/CHANGELOG.rst)
- [Commits](marshmallow-code/marshmallow@3.5.2...3.6.0)

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