Ensure that issuing update notices works for Burst and SSM events

From ligo-followup-advocate!181 (comment 1218878)

Somewhat related to this MR: currently update notices require pointing towards some P_astro and EM_bright files: https://emfollow.ligo.caltech.edu/gwcelery/#issue-update-gcn-notice Not sure if that machinery will need to be changed to accomodate SSM alerts (or even Burst alerts now that I think about it).

Edited Dec 11, 2024 by Brandon Piotrzkowski

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