Update h2 requirement from <=4.2.0,>=4.1 to >=4.1,<=4.3.0 (#7852)
* Update h2 requirement from <=4.2.0,>=4.1 to >=4.1,<=4.3.0
Updates the requirements on [h2](https://github.com/python-hyper/h2) to permit the latest version.
- [Changelog](https://github.com/python-hyper/h2/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/python-hyper/h2/compare/v4.1.0...v4.3.0)