Build snapshot release for demo branches (#292)

## Changes

Idea: we use `demo-*` branches for demo-able builds that are not yet
ready to be merged.

## Tests

n/a

.github/workflows/release-snapshot.yml

@@ -3,7 +3,8 @@ name: release-snapshot
 on:
   push:
     branches:
-      - main
+      - "main"
+      - "demo-*"
 
   workflow_dispatch: