Github notifications cease after renaming repo

### Description

An established room was set up to receive various notifications for `repo1`, when later that repo changed it's name to `repo2`. Notifications ceased.

In Scalar (or is it Modular now?), the old repo name was present under "Existing Webhooks". To get notifications working again I had to enable the new repo, close Scalar, open Scalar again, uncheck the new repo, and re-check it. There's probably a few steps I could have avoided, but those are the steps I took to fix the issue.

Worth noting: After checking off the new repo the first time, the webhook URL was missing in Github. This is what triggered me to toggle it off/on again.

### Steps to reproduce

- Have a Github repo set to notify about activity in a room
- Rename that repo

I would expect the notifications to seamlessly work, or at the very least indicate some kind of problem in Scalar when I go to check the Github settings. There also shouldn't need to be some toggling of settings to get the webhook to be re-added: It should just be magic the first time.

Log: not sent

### Version information

- **Platform**: web (in-browser)
- **Browser**: Chrome 60
- **OS**: Windows 10
- **URL**: riot.im/develop