Gitlab CODEOWNERS with custom groups doesn't parse

### Environment

SaaS ([https://sentry.io/]())

### Steps to Reproduce

Import a Gitlab `CODEOWERS` from connected repo that has named sections with a default owner that maps to mapped teams. eg. we have something that looks something like this:

```
[Team Core] @org/team-core
folder-1/

[Team Other] @org/team-other
folder-2/
```

### Expected Result

Should parse the CODEOWNERS file and rules correctly, and assign the code that it is owned to the correct team or person.
The documentation about this syntax is here: [https://docs.gitlab.com/user/project/codeowners/reference/#set-default-code-owner-for-a-section]()

### Actual Result

Got an error banner that reads

> There was 1 ownership issue within Sentry on the latest sync with the CODEOWNERS file
>
> The following usernames do not have an association in the organization: org-name
**Core\]**

And there is a new codeowner entry in the ownership table called `[Team`

### Product Area

Settings - Projects

### Link

https://{ORG_SLUG}.sentry.io/settings/projects/{PROJECT_SLUG}/ownership/

### DSN

[https://42a75d0589aa4085b0a6b61a48f8bead@o1301086.ingest.sentry.io/6570851]()

### Version

*No response*

Start by locating the GitLab CODEOWNERS parser used during repository ownership sync, then reproduce the issue with the named-section example containing default owners. Confirm that sections such as [Team Core] are parsed as sections and that folder-1/ and folder-2/ map to the intended teams or people without an ownership error.

Written by the indexing model from the issue text.