fix(ci): enable non-cone mode for sparse-checkout of single file

Git sparse-checkout in cone mode (default) only accepts directories.
Adding sparse-checkout-cone-mode: false allows checking out individual
files like docker-compose.yml.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ggfevans

.github/workflows/deploy-prod.yml

@@ -170,6 +170,7 @@ jobs:
         with:
           sparse-checkout: |
             docker-compose.yml
+          sparse-checkout-cone-mode: false
 
       - name: Sync docker-compose.yml to prod
         run: |