This is essentially the same fix as #161740, except not just for macOS.
The `dnspython` build was failing on Linux with a certificate
verification failure just like in #161740:
```ShellSession
$ nix build nixpkgs#python3Packages.dnspython --rebuild
error: builder for '/nix/store/c1v553fzq3yybsd0lm398qf87jmy47qd-python3.10-dnspython-2.3.0.drv' failed with exit code 1;
last 10 log lines:
>
> /nix/store/iw1vmh509hcbby8dbpsaanbri4zsq7dj-python3-3.10.10/lib/python3.10/ssl.py:1342: SSLCertVerificationError
…
```
… and this change fixes that build failure.
509f32d9c9