fix: correct publish workflow branch filter

The workflow_run trigger was watching `master` but the default
branch is `main`, so auto-publishing never fired.

Author: tortmayr

.github/workflows/publish.yml

@@ -5,7 +5,7 @@ on:
     workflows: ['CI']
     types:
       - completed
-    branches: [master]
+    branches: [main]
   workflow_call:
     inputs:
       ref: