GH webhook secret expires without refresh

- Returns 403 error ([line 93 in github.handler.ts](https://github.com/calcom/synclinear.com/blob/4ebfa1408a90dd23584a2f50e6f1a1e2f164fda3/utils/webhook/github.handler.ts#L98))
- Currently, must manually update the token in `githubRepo.webhookSecret` and [GH repo] > Settings > Webhooks > SyncLinear.com > Webhook Secret
- Should automatically refresh token on a schedule or upon failure