Only print the tag when the received reference has a tag, if
we can't cast the received tag to a `reference.Tagged` then
skip printing the tag as it's likely a digest.
Fixes panic when trying to install a plugin from a reference
with a digest such as
`vieux/sshfs@sha256:1d3c3e42c12138da5ef7873b97f7f32cf99fb6edde75fa4f0bcf9ed277855811`
Signed-off-by: Laura Brehm <laurabrehm@hey.com>