Dont use latest version of raven until gracedb-sdk decision is reached

ligo-raven 3.0 moved back to gracedb-client from gracedb-sdk. This is my fault as I was under the impression everybody was in agreement that we'd use gracedb-client in O4. This MR pins ligo-raven at >=2.0 and <3.0, and can be undone once a decision is made about gracedb-client vs gracedb-sdk. Either we'll remove gracedb-sdk and we can upgrade to raven 3.0, or we'll stick with gracedb-sdk and Brandon will delete this version of raven from PyPi so we can drop the pin.

This MR will fix this issue: https://sentry.io/organizations/ligo-caltech/issues/3779174504/events/fa96b2a5af6d4bb5b1afaae7586d8a53/