Fix NoMethodError in Vulnerabilities::RemoveAllVulnerabilitiesWorker

What does this MR do and why?

Fix NoMethodError in Vulnerabilities::RemoveAllVulnerabilitiesWorker

Related to #433119 (closed)

How to set up and validate locally

1. echo "Feature.enable(:enable_remove_all_vulnerabilties_from_project_mutation)" | rails c
2. Create a new project and populate it with Vulnerabilities. You can use https://gitlab.com/gitlab-examples/security/security-reports project to do this quickly.
3. Note down project ID
4. Run the following mutation

mutation {
  vulnerabilitiesRemoveAllFromProject(input: { projectIds: ["gid://gitlab/Project/PROJECT_ID_HERE"]}) {
    projects {
      id
    }
  }
}

1. Go to /-/security/vulnerability_report, it should be empty

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.