Thanks for the fix, Victor.

Sometime after filing this, I remembered that we had seen a similar problem some years ago and found bpo-21572 in which I had changed Lib/site.py to no longer use a release-dependent URL for the license file - which is why the check to skip if on a pre-release had been added previously to test_license_exists_at_url. So I should have removed the skip in test_site at the same time as it is no longer needed and hides problems like this until the final release.  PR 22688 and its backports remove the skip.