Take too long for sync big github repo

**Describe the bug**
When you [sync](https://codepo.xyz/github/sync-repo/) a big GitHub repository to codepo (such as [this repository](https://github.com/boyuan12/GitHub-Clone)), it will take more than 30 seconds, which will cause a timeout error as writtened on [Heroku](https://devcenter.heroku.com/articles/request-timeout).

**To Reproduce**
Steps to reproduce the behavior:
1. Sign in to [Codepo](https://codepo.xyz)
2. Click on "Sync with GitHub"
3. Login if prompted
4. Type username and password. To make this error happen, type username: boyuan12, repo: GitHub-Clone
5. You should see the error due to timeout

**Expected behavior**
It should works similarly to small repository that take less than 30 sec to fetch. For example, username: boyuan12, repo: APOD

**Screenshots**
N/A

**Desktop (please complete the following information):**
- OS: Mac
- Browser Chrome
- Version Version 89.0.4389.114 (Official Build) (x86_64)

**Additional context**
N/A

Reproduce the timeout through the “Sync with GitHub” flow using the GitHub-Clone repository, and compare it with the smaller APOD repository. Read the sync request path and Heroku request-timeout guidance first; done means that syncing the reported large repository completes without a timeout.

Written by the indexing model from the issue text.