CDN purges don't purge all files.

[Yhg1s]

Currently, we purge the CDN cache for a couple of files, but not all the files (notably missing are new files added relatively recently: sboms and sigstore signatures). https://github.com/python/release-tools/blob/master/run_release.py#L931

We should update that list, or just list all files on the download server and purge all of them.

[Yhg1s]

The PR fixes the notably missing files, but still does not purge all the files (e.g. the files in the arm, amd64 and win32 subdirectories).