Track: Inconsistent behavior in .git directory compared to `git add`

`git add` doesn't allow you to run it when in a `.git` directory.

```
$ cd repo/.git
$ git add ../some.file
fatal: This operation must be run in a work tree
$ echo "$?"
128
```

`git lfs track` doesn't care and creates a `.gitattributes` file in `repo/.git`.
