Increase retries when grabbing Fermi sky maps

Due to the fact that Fermi sky maps typically become available ~1.5 minutes after GCN notices go out, we need to increase our timeout when trying to grab them (note that we have not successfully grabbed an Fermi sky map on playground, only when trying long after the notice has gone out on local computers).

We will also try to catch URLErrors (https://sentry.io/organizations/ligo-caltech/issues/1334504857/?project=1425216&query=is%3Aunresolved) and remove the max retries (5) present before, instead opting to wait for 10 minutes which should be plenty of time.