Bump dnspython from 2.1.0 to 2.6.0

Bumps [dnspython](https://github.com/rthalley/dnspython) from 2.1.0 to 2.6.0.
- [Release notes](https://github.com/rthalley/dnspython/releases)
- [Changelog](https://github.com/rthalley/dnspython/blob/master/doc/whatsnew.rst)
- [Commits](rthalley/dnspython@v2.1.0...v2.6.0)

---
updated-dependencies:
- dependency-name: dnspython
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>