Update dismissal_reason on vulnerabilityDismiss

What does this MR do and why?

Update dismissal_reason on vulnerabilityDismiss when vulnerability is already dismissed.

Related issue: #394694 (closed)

Example of usage

Request

mutation {
  vulnerabilityDismiss( input: {id: "gid://gitlab/Vulnerability/582", dismissalReason: ACCEPTABLE_RISK}){
    vulnerability {
      state
      stateTransitions {
        nodes {
          dismissalReason
	  createdAt
	  fromState
          toState
        }
      }
    }
  }
}

Response

{
  "data": {
    "vulnerabilityDismiss": {
      "vulnerability": {
        "state": "DISMISSED",
        "stateTransitions": {
          "nodes": [
            {
              "dismissalReason": ACCEPTABLE_RISK,
              "createdAt": "2023-03-17T11:11:33Z",
              "fromState": "DISMISSED",
              "toState": "DISMISSED"
            },
            {
              "dismissalReason": NOT_APPLICABLE,
              "createdAt": "2023-03-15T11:11:33Z",
              "fromState": "DETECTED",
              "toState": "DISMISSED"
            },
            {
              "dismissalReason": null,
              "createdAt": "2023-03-15T11:10:45Z",
              "fromState": "DISMISSED",
              "toState": "DETECTED"
            },
            {
              "dismissalReason": null,
              "createdAt": "2023-03-15T11:10:00Z",
              "fromState": "DETECTED",
              "toState": "DISMISSED"
            }
          ]
        }
      }
    }
  }
}

Error Response

{
  "data": {
    "vulnerabilityDismiss": null
  },
  "errors": [
    {
      "message": "To state must not be the same as from_state for similar dismissal_reason",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "vulnerabilityDismiss"
      ]
    }
  ]
}

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.