Background fetch causes freeze for roughly a second

**Describe the bug**
If you set this in your config:
```yml
refresher:
fetchInterval: 1
```

And then just navigate around lazygit e.g. navigating through the list of commits, you'll notice just how frequently lazygit pauses as part of a fetch, blocking the UI thread. This is super annoying!

The background fetch should not have this big of an impact on the UI