Update zaza's webhook with readthedocs (due to secrets change) by 2024-01-31!

[ajkavanagh]

See Security update on incoming webhooks from integrations for details.

Basically, it’s going to stop working on the 2024-01-31.

It just needs to be updated according to How to manually configure a Git repository integration and use the secret from the readthedocs integration: https://readthedocs.org/dashboard/zaza/integrations/39183/