Update CI workflow to exclude 'main' branch

Remove 'main' branch from CI workflow triggers.

Signed-off-by: Ryan Baxter <ryan.baxter@broadcom.com>

Author: ryanjbaxter

.github/workflows/ci.yaml

@@ -4,7 +4,6 @@ name: Spring Cloud Release CI Job
 on:
   push:
     branches:
-      - main
       - 2025.0.x
 
   # Scheduled builds run daily at midnight UTC