allowed_url: implement deref

Since this is a validated wrapper around Url, dereferencing the
actual Url is handy
7 jobs for aurl in 28 minutes and 6 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #187987
fedora test

00:07:25

 
  Lint
manual #187989
allowed to fail manual
clippy
passed #187988
rustfmt

00:00:40

passed #187990
tarball

00:10:56

 
  Cross Distro
passed #187993
debian_i386:testing

00:09:42

passed #187992
debian:testing

00:09:07

passed #187991
fedora:rawhide

00:08:37