Ensure pulumi history marks secrets that can't be un-encrypted as such

[stack72]

This changes this:

▶ pulumi stack history --json --show-secrets
error: bad value

to this

▶ pulumi stack history --json --show-secrets
[
  {
    "kind": "update",
    "startTime": "2020-11-06T00:20:16.000Z",
    "message": "",
    "environment": {
      "exec.kind": "cli"
    },
    "config": {
      "aws:region": {
        "value": "us-east-1",
        "secret": false
      },
      "history:MySecretPassword": {
        "value": "Password1234!",
        "secret": true
      }
    },
    "result": "succeeded",
    "endTime": "2020-11-06T00:20:29.000Z",
    "resourceChanges": {
      "same": 1,
      "update": 1
    }
  },
  {
    "kind": "import",
    "startTime": "2020-11-06T00:19:28.000Z",
    "message": "",
    "environment": {},
    "config": {},
    "result": "succeeded",
    "endTime": "2020-11-06T00:19:29.000Z",
    "resourceChanges": {
      "create": 0,
      "delete": 0,
      "same": 2,
      "update": 1
    }
  },
  {
    "kind": "update",
    "startTime": "2020-11-06T00:02:29.000Z",
    "message": "",
    "environment": {
      "exec.kind": "cli"
    },
    "config": {
      "aws:region": {
        "value": "us-east-1",
        "secret": false
      },
      "history:MySecretPassword": {
        "value": "ERROR_UNABLE_TO_DECRYPT",
        "secret": true
      }
    },
    "result": "succeeded",
    "endTime": "2020-11-06T00:02:43.000Z",
    "resourceChanges": {
      "create": 2
    }
  }
]

[EvanBoyle]

Awesome, thanks for the quick resolution on this!