title: React-Query mutation.error not recognized as type Error
body: <p>When using a React-Query mutation, I have a component that displays an error message. but Typescript doesn't recognize the mutation.error property as type Error:</p>
  <pre><code>if (mutation.isError){
      console.log(mutation.error.message);             // Property 'message' does not exist on type 'unknown'.
      console.log((mutation.error as Error).message);  // works
  }
  </code></pre>
  <p>How can I inform typescript that mutation.error is indeed an Error object?</p>