[prefer-spy-on] incorrect autofix 

The following code gets wrongly autofixed by the `jest/spy-on` rule:

```ts
foo[bar] = jest.fn().mockReturnValue(undefined)
```

Actual behavior:

```ts
jest.spyOn(foo, 'bar').mockImplementation().mockReturnValue(undefined)
```

Expected behavior:

```ts
jest.spyOn(foo, bar).mockImplementation().mockReturnValue(undefined)
```