Use descriptive URIs in 104 Warning messages

Use descriptive URIs in 104 Warning messages

This makes the new GPG related warnings much nicer to read,
for example, the second one here replaces the first one:

W: gpgv:/var/lib/apt/lists/example.com_dists_stable_InRelease: Weak ...
W: http://example.com/dists/stable/InRelease: Weak ...