Remove scannerType argument from Mutations::Vulnerabilities::Create

What does this MR do?

When verifying work done on Directly create vulnerability records via API it came to our attention that the mutation accepts an superfluous argument – scannerType

Screenshot

How to setup and validate locally (strongly suggested)

1. Enable the invite modal

   Feature.enable(:create_vulnerabilities_via_api)

2. Go to GraphQL Explorer http://127.0.0.1:3000/-/graphql-explorer
3. Try supplying scannerType as an argument to the mutation

mutation vulnerabilityCreate($input: VulnerabilityCreateInput!) {
  vulnerabilityCreate(input: $input) {
    errors
    clientMutationId
    vulnerability: vulnerability {
      id
      vulnerabilityPath
      project {
        id
        fullPath
      }
    }
  }
}

{
  "input": {
    "project": "gid://gitlab/Project/6102100",
    "title": "A manual vulnerability number 2",
    "description": "A descriptive description",
    "scannerType": "SAST",
    "scannerName": "Thiago",
    "state": "CONFIRMED",
    "identifiers": [
      {
      	"name": "CVE-3",
      	"url": "http://localhost"
    	}
    ]
  }
}

It should complain about VulnerabilityCreateInput not having a scannerType field.

Does this MR meet the acceptance criteria?

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• This change is backwards compatible across updates, or this does not apply.

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• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.