Bump idna from 2.5 to 2.8
Bumps [idna](https://github.com/kjd/idna) from 2.5 to 2.8.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](https://github.com/kjd/idna/compare/v2.5...v2.8)
Signed-off-by: dependabot-preview[bot] <[email protected]>