"v" prefix is prepended to tag when it shouldn't be

[ludfjig]

Describe the bug

#2890 introduced a bug which where it appends a "v" prefix where it shouldn't. In the case that the tag is "latest", or when a tag is missing.

To Reproduce

porter explain -r ghcr.io/getporter/examples/porter-hello and
bin/porter explain -r ghcr.io/getporter/examples/porter-hello:latest will try fetch tag :v and :vlatest, respectively

Expected behavior

No v should be prepended in these cases

Porter Command and Output

$ porter [e.g. install --param foo=bar --credential-set azure]
lots of output

Version

Copy the output of porter version below

[e.g. porter v0.14.1-beta.2 (72dd5df)]