GraphQL: Querying user workspaces for a different user shows workspaces of logged-in user

Problem

Given the following GraphQL query:

query {
  user(username:"gitlab.mschoenlaub") {
    id
    workspaces {
      nodes {
        name
        user {
          id
        }
        actualState
      }
    }
  }
}

Logged in as @splattael I see a list of workspaces from logged-in user:

Proposed solution

Error out if showing workspaces for different users is not possible.