build(deps): bump dnspython in /regression-tests.ixfrdist

build(deps): bump dnspython in /regression-tests.ixfrdist

Bumps [dnspython](https://github.com/rthalley/dnspython) from 2.1.0 to 2.6.1.
- [Release notes](https://github.com/rthalley/dnspython/releases)
- [Changelog](https://github.com/rthalley/dnspython/blob/main/doc/whatsnew.rst)
- [Commits](https://github.com/rthalley/dnspython/compare/v2.1.0...v2.6.1)

---
updated-dependencies:
- dependency-name: dnspython
  dependency-type: direct:production
...

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