GitHub Integration Problem

### Environment

SaaS (https://sentry.io/)

### Steps to Reproduce

1. Add GitHub integration to an organization and during the GitHub flow select only specific repositories.
2. Proceed happily.
3. Realize you have a new repository you want to grant Sentry access to; clicking Configure by the installation doesn't let you do that. Clicking Add Installation to go back through the same re-linkage results in a "We noticed you already integrated with GitHub! Do you want to connect an existing GitHub organization to this Sentry organization or connect a new one?" - if you select the already-connected organization, you are taken to an upgrade billing screen.

### Expected Result

If re-selecting the same GitHub org, the user should be presumed to be asking to re-configure their existing install.

### Actual Result

User was presumed to want to integrate with multiple GitHub orgs/installs, which wasn't the case.

### Product Area

Settings - Repositories

### Link

https://network-weather.sentry.io/settings/integrations/github/

### DSN

_No response_

### Version

_No response_

Start by reproducing the GitHub integration flow from the linked Sentry settings page, selecting specific repositories and then trying to add another. Trace the Configure and Add Installation paths to determine where an already-connected GitHub organization is treated as a new installation; done means reselecting it opens reconfiguration without sending the user to billing.

Written by the indexing model from the issue text.