Seer integration fails to save selected repo

### Environment

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

### Steps to Reproduce

When attempting to configure Seer for a Sentry project and add a repository, the selection is not persisted. The network request to the Seer preferences API returns a 500 Internal Server Error, and on refresh the repo is gone.

1. Open Console
2. Navigate to `https://.sentry.io/settings/projects//seer/`
3. Click Add Repos
4. Choose a repository
5. Click Done
6. Observe in Console:

`POST https://us.sentry.io/api/0/projects//seer/preferences/ 500 (Internal Server Error)`

### Expected Result

The selected repository should be saved

### Actual Result

The repo selection is lost upon refresh

### Product Area

Unknown

### Link

*No response*

### DSN

*No response*

### Version

*No response*