the commit one release after the content released as v5.17.7

What?

Well, normally when we release perl, we do the final bits of work on
a branch other than blead.  That branch then gets tagged, then it's
merged into blead.  There was a problem with that process, this time.

The branch was rebased before merging — which is fine — but that
rebase was done after the tagging, and the tag was not moved.  This
led to a v5.17.7 tag that was not an ancestor of blead, which was
going to lead to problems in the future.  For example, git-describe
would not show the proper previous version, and bisects would not
work as expected.

Rather than create a merge commit, I (rjbs) deleted the old tag and
put moved it to 3cf48ca.  This means that while most users will see
the tag in line with blead, some will not.  This main practical
effect of this (because the trees are the same) is that git-describe
will be confused or confusing.  Rather than suffer through that,
this tag was added.  There was no v5.17.7.0 release of perl.

We do not anticipate *ever* doing this again.