Checking if ski-6.13.tar.gz was modified since original release.

Over at Homebrew, we were trying to update our packages for Monterey and noticed that the ski v6.13 tarball was reporting a different checksum (tracker for all similar issues: https://github.com/Homebrew/homebrew-core/issues/88329)

I see that the v6.13 tarball was originally added back in Oct 2019: https://github.com/Homebrew/homebrew-core/pull/45573

From the NEWS, I see that it says Sep 2021, so I am guessing it was modified in-place: http://www.catb.org/~esr/ski/NEWS

We mainly want to make sure there are no malicious circumstances and confirm that the modification was intentional.

Thanks.