Bump marshmallow from 3.12.1 to 3.12.2

Bumps [marshmallow](https://github.com/marshmallow-code/marshmallow) from 3.12.1 to 3.12.2.
- [Release notes](https://github.com/marshmallow-code/marshmallow/releases)
- [Changelog](https://github.com/marshmallow-code/marshmallow/blob/dev/CHANGELOG.rst)
- [Commits](marshmallow-code/marshmallow@3.12.1...3.12.2)

---
updated-dependencies:
- dependency-name: marshmallow
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]