Ambiguity if a branch and tag have the same name

[JonathonReinhart]

@xanarin pointed out that Git allows a tag and a branch to have the same name. So the fix in #16 introduces a potential ambiguity, by no longer allowing tags/v1.2.3.

The problem is that the GitLab list project pipelines API just says ref, and I've proven that you cannot pass tags/foo:

>>> p.pipelines.list(ref='v8.4.8-1')
[<ProjectPipeline id:20692>, <ProjectPipeline id:20685>, <ProjectPipeline id:20639>, <ProjectPipeline id:20638>, <ProjectPipeline id:20478>]
>>> p.pipelines.list(ref='tags/v8.4.8-1')
[]

The API does however provide scope:

Attribute	Type	Required	Description
scope	string	no	The scope of pipelines, one of: running, pending, finished, branches, tags

So perhaps we could look at the ref to see if tags/ is present, and if so, strip it, and then pass scope=tags.

[JonathonReinhart]

Actually, there appears to be a bug in GitLab!

If you push a branch that has the same name as an existing tag, then GitLab will run a pipeline for the correct commit, but incorrectly thinks the pipeline is for "a tag" (the tag attribute on the returned pipeline object is true).

Even more confusing, scope='tags' returns an incorrect list in this case.

I opened this issue with gitlab.