Bump dnspython from 2.5.0 to 2.6.1

Bumps [dnspython](https://github.com/rthalley/dnspython) from 2.5.0 to 2.6.1.
- [Release notes](https://github.com/rthalley/dnspython/releases)
- [Changelog](https://github.com/rthalley/dnspython/blob/main/doc/whatsnew.rst)
- [Commits](rthalley/dnspython@v2.5.0...v2.6.1)

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

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

requirements.txt

@@ -1,6 +1,6 @@
 BTrees==5.2
 cffi==1.16.0
-dnspython==2.5.0
+dnspython==2.6.1
 mysql-connector==2.2.9
 persistent==5.2
 pycparser==2.21