In workflow download the inputs have a non empty workflow_outputs section

[lldelisle]

Describe the bug
If you create a workflow in the workflow editor and you download it as ga file. Inputs will have an workflow_outputs section, for example:

{
    "a_galaxy_workflow": "true",
    "annotation": "",
    "format-version": "0.1",
    "name": "Test",
    "steps": {
        "0": {
            "annotation": "",
            "content_id": null,
            "errors": null,
            "id": 0,
            "input_connections": {},
            "inputs": [],
            "label": null,
            "name": "Input dataset",
            "outputs": [],
            "position": {
                "left": 0,
                "top": 0
            },
            "tool_id": null,
            "tool_state": "{\"optional\": false, \"tag\": \"\"}",
            "tool_version": null,
            "type": "data_input",
            "uuid": "9a0698ef-46dc-40e6-a53c-6a94324b9619",
            "workflow_outputs": [
                {
                    "label": null,
                    "output_name": "output",
                    "uuid": "27f2e5df-41ec-4132-aa38-9f54afc6b7bc"
                }
            ]
        },
        "1": {
            "annotation": "",
            "content_id": "toolshed.g2.bx.psu.edu/repos/bgruening/text_processing/tp_head_tool/1.1.0",
            "errors": null,
            "id": 1,
            "input_connections": {
                "infile": {
                    "id": 0,
                    "output_name": "output"
                }
            },
            "inputs": [
                {
                    "description": "runtime parameter for tool Select first",
                    "name": "infile"
                }
            ],
            "label": null,
            "name": "Select first",
            "outputs": [
                {
                    "name": "outfile",
                    "type": "input"
                }
            ],
            "position": {
                "left": 268,
                "top": 57
            },
            "post_job_actions": {},
            "tool_id": "toolshed.g2.bx.psu.edu/repos/bgruening/text_processing/tp_head_tool/1.1.0",
            "tool_shed_repository": {
                "changeset_revision": "ddf54b12c295",
                "name": "text_processing",
                "owner": "bgruening",
                "tool_shed": "toolshed.g2.bx.psu.edu"
            },
            "tool_state": "{\"complement\": \"\", \"count\": \"10\", \"infile\": {\"__class__\": \"RuntimeValue\"}, \"__page__\": null, \"__rerun_remap_job_id__\": null}",
            "tool_version": "1.1.0",
            "type": "tool",
            "uuid": "bb7e2009-79c8-4259-a42d-4b81facd4e52",
            "workflow_outputs": [
                {
                    "label": null,
                    "output_name": "outfile",
                    "uuid": "80934b02-3ede-40c5-b3b8-3b60762a1d6f"
                }
            ]
        }
    },
    "tags": [],
    "uuid": "1eaeda3b-9439-4aa7-aa1f-88ede4ef4218",
    "version": 1
}

Galaxy Version and/or server at which you observed the bug
usegalaxy.org
Galaxy Version: {"version_major":"22.05","version_minor":"1"}

To Reproduce
Steps to reproduce the behavior:

1. Create a simple workflow with an input
2. Download as .ga
3. Inspect the step 0

Expected behavior
I would like to have: "workflow_outputs": [] for inputs.
This behaviour seems to be inconsistent. Sometimes I get an empty workflow_outputs and sometimes I get a label: null workflow output.

Additional context
See davelopez/galaxy-workflows-vscode#55

[lldelisle]

For info, If I reupload this workflow, and download it, I now have:
"workflow_outputs": [] for inputs...

[mvdbeek]

We probably don't want to return workflow_outputs for workflow inputs without a label.