using same string for branch and tag fails.

### Jenkins and plugins versions report

Environment

```text
Paste the output here
```

### What Operating System are you using (both controller, and any agents involved in the problem)?

controller - centos 6.4
agent - irrelevant (issue is related to plugin implementation on controller)

### Reproduction steps

1. create a repo in gitlab.
2. create a multibranch pipeline on jenkins, pointing to the repo from step 1. configure the job to "see" all branches and all tags, and run the Jenkinsfile in the root folder.
3. create a branch called "some_version".
4. check that jenkins "sees" the branch and runs it's jenkinsfile.
5. create a tag called "some_version".

### Expected Results

the tag should appear under tags in the job created before, and should run just like any other tag.

### Actual Results

the job fails to "see" the tag, and nothing happens.

### Anything else?

looking in the file system on the controller, I see that both branches and tag are created as folders under the job itself. I guess that's why using the same string for both tags and branch doesn't work.
suggestion - add another level of separation in the folders (branches/tags/merge_requests) and it will solve it...