There is a bug report for r834073, therefore add a CHANGES entry.

Fix litmus warning: According to RFC2518, COPY to non-existant collection
should give 409 CONFLICT.

PR: 39299


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@834107 13f79535-47bb-0310-9956-ffa450edef68