This is the third patch in the series.  Description
from patch:

  This way, there's no risk of accidentally reusing a
  port number used by another test.  This changes the
  workings of the "/*.narinfo for a compressed file" test
  a little, by not reusing the port from the test
  "/*.narinfo with compression".

  * tests/publish.scm
    (*latest-port*, call-with-guix-publish, with-guix-publish):
    automatically assign port numbers, and change tests to
    use the new calling rules.