chore(ci): disable release-please on fork

Fork doesn't publish releases. Point trigger at non-existent branch
to prevent unwanted release PRs on every push to main.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: omalleyandy

.github/workflows/release-please.yml

@@ -1,7 +1,7 @@
 on:
   push:
     branches:
-      - main
+      - disabled-on-fork
 
 permissions:
   contents: write