Attempts to "Download the artifacts archive" for a tag ref via the Jobs API is failing with a "404 Not found"
### Overview
We're attempting to [download the artifacts archive](https://docs.gitlab.com/ee/api/jobs.html#download-the-artifacts-archive) via the following URL:
```
GET /projects/:id/jobs/artifacts/:ref_name/download?job=name
```
We're seeing this fail with the following error:
```
{"message":"404 Not found"}
```
When attempting to use a tag as the `ref_name`.
### Components
We're using the following:
* The `v4` Jobs API
* The GitLab Shared Runner
### Test Cases
A few notes for background:
* :white_check_mark: Attempts to download artifacts on the `master` ref works correctly: `GET /projects/:id/jobs/artifacts/master/download?job=name`
* :white_check_mark: Attempts to download the artifacts from the expected job ID also works correctly: `GET projects/:id/jobs/:job_id/artifacts`
* :no_entry_sign: Attempts to download artifacts with the specific tag as a `ref` fail.
I can, however confirm that these artifacts are available for this ref by running the following command:
```
curl -H"PRIVATE-TOKEN: XXXXXXXX" https://gitlab.com/api/v4/projects/12345678/jobs/000111222
```
Which returns a response like the following:
```json
{
"id": 000111222,
"status": "success",
"stage": "build",
"name": "build-zip",
"ref": "0.3.0",
"tag": true,
"created_at": "2020-04-28T12:56:51.203Z",
"artifacts_file": {
"filename": "artifacts.zip",
"size": 371601
},
"artifacts_expire_at": null
}
```
My expectation [from the documentation](https://docs.gitlab.com/ee/api/jobs.html#download-the-artifacts-archive) is that the following command should work:
```
curl -H"PRIVATE-TOKEN: XXXXXXXX" https://gitlab.com/api/v4/projects/12345678/jobs/artifacts/0.3.0/download?job=build-zip
```
Since it is a valid tag ref with a valid artifacts file. Instead, it fails with the following:
```
{"message":"404 Not found"}
```
This was working for previous tags for us, so I'm not sure if it's due to a regression here?
issue