OAuth: re-enable sync active user repos task (#12443)
- Take into consideration active users from the last 30 days only.
- Ignore GitHub App, so we don't re-sync installations over and over
again, as users can share the same installation, and repos from the GH
app are kept in sync via a webhook.
This task now completes in 42 minutes.
Closes https://github.com/readthedocs/readthedocs.org/issues/12406
