Racket v8.6 Release Thread

Mea culpa, both the problem (the removal of the trailing slash) and the "solution" (that is, the re-tagging) are my responsibility. One challenge in testing this manual makefile update are that the catalog itself must be available in order to test it, which is why this update occurs after testing is complete. One solution would be to use two tags for each release, to allow testing before the application of the final tag.

Historically, the github tags have not actually been a principal component of the release. Perhaps in this case it would be simpler just to delete the v8.6 github tag altogether. Thoughts?