typescript-eslint/unbound-method when mocking window.URL.createObjectURL

I am trying to get my unit test working. It currently fails with:

TypeError: URL.createObjectURL is not a function

I eventually stumble upon:

• Jest URL.createObjectURL is not a function

So I am now providing the following mock:

  test('my test', async (): Promise<void> => {
    window.URL.createObjectURL = (object: any): string => object.toString();

However this makes eslint reports now:

Avoid referencing unbound methods which may cause unintentional scoping of `this`.

Even after reading twice:

• https://github.com/typescript-eslint/typescript-eslint/blob/v2.24.0/packages/eslint-plugin/docs/rules/unbound-method.md

It feels like (object: any): string => object.toString() is correct here. What am I missing / misunderstanding ?