Deploying to Firebase hosting in a Github Action for a SPA.
In my case this was working and magically stopped working. Strangely enough the referenced error pertained to functions even though this was hosting deployment.
In cloud.google.com click 'IAM & Admin', then look for the principal with 'github-action', hit the pencil to edit, click 'add another role' and add 'cloud functions viewer'. BTW, make sure you're in the right project (i have multiple)
You need to add Cloud Function Viewer access to all Github Action Service Accounts in the GCP IAM Console