config wizard does not work if ~/.config/git/config contains include statements

Steps to reproduce:

* Make sure `~/.git` does not exist
* Create ~/.config/git/config` with a least two includes, like so:

```ini
[include]
path = /path/to/1
path = /path/to/2
```
Run `git-repo config`, do the oauth dance.

Nothing is stored.

PS: I think this is a bug in the code that reads and writes git config. If I were you, I'll just run
`git config --get foo.bar` and `git config --global foo.bar 42` instead of using a re-implementation of git config parsing in Python.

Reproduce the issue by creating ~/.config/git/config with two include entries, ensuring ~/.git is absent, and running git-repo config through the OAuth flow. Trace the Python code that reads and writes Git configuration, then verify that the configuration is stored successfully when include statements are present.

Written by the indexing model from the issue text.