charmhub install action of refresh returns track only for effective-channel

[Heather Lanigan]

Charms without a default channel are returning a risk only for the effective-channel with the install action of refresh. This creates an ambiguous response.

$ curl -s https://api.snapcraft.io/v2/charms/refresh -H 'Content-type: application/json' -d '{"context":[],"actions":[{"action":"install","instance-key":"4c46917e-3006-4fec-8a06-5eba393fa4cd","name":"ubuntu","channel":"stable","base":{"architecture":"amd64","name":"ubuntu","channel":"20.04"}}],"fields":["bases","config-yaml","download","id","license","metadata-yaml","name","publisher","resources","revision","summary","type","version"]}' | jq
{
  "error-list": [],
  "results": [
...
      },
      "effective-channel": "stable",
      "id": "DksXQKAQTZfsUmBAGanZAhpoS4dpmXel",
      "instance-key": "4c46917e-3006-4fec-8a06-5eba393fa4cd",
      "name": "ubuntu",
      "released-at": "2022-06-30T17:12:55.757188+00:00",
      "result": "install"
    }
  ]
}

$ curl -s https://api.snapcraft.io/v2/charms/refresh -H 'Content-type: application/json' -d '{"context":[],"actions":[{"action":"install","instance-key":"4c46917e-3006-4fec-8a06-5eba393fa4cd","name":"ubuntu","channel":"latest/stable","base":{"architecture":"amd64","name":"ubuntu","channel":"20.04"}}],"fields":["bases","config-yaml","download","id","license","metadata-yaml","name","publisher","resources","revision","summary","type","version"]}' | jq
{
  "error-list": [],
  "results": [
    {
...
      "effective-channel": "latest/stable",
      "id": "DksXQKAQTZfsUmBAGanZAhpoS4dpmXel",
      "instance-key": "4c46917e-3006-4fec-8a06-5eba393fa4cd",
      "name": "ubuntu",
      "released-at": "2022-06-30T17:12:55.757188+00:00",
      "result": "install"
    }
  ]
}

Not a problem is the charm has a default channel:

curl -s https://api.snapcraft.io/v2/charms/refresh -H 'Content-type: application/json' -d '{"context":[],"actions":[{"action":"install","instance-key":"heather-testing","name":"mysql-router","base":{"architecture":"amd64","name":"ubuntu","channel":"20.04"},"channel":"8.0"}]}' | jq
{
  "error-list": [],
  "results": [
    {
...
      "effective-channel": "8.0/stable",
      "id": "CjjVf4bSJGT6rKjg7Qk3EZteCoEhKXHh",
      "instance-key": "heather-testing",
      "name": "mysql-router",
      "released-at": "2022-08-05T19:05:33.072115+00:00",
      "result": "install"
    }
  ]
}