ci: build PR test deployments with staging schema (#6866)

PR test envs run core unstable/unreleased main, so the released schema
breaks against them.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: lkostrowski

.github/workflows/pr-automation.yml

@@ -143,6 +143,8 @@ jobs:
           IS_CLOUD_INSTANCE: true
           ENABLED_SERVICE_NAME_HEADER: true
           ONBOARDING_USER_JOINED_DATE_THRESHOLD: ${{ vars.STAGING_ONBOARDING_USER_JOINED_DATE_THRESHOLD }}
+          # PR test envs run core unstable/unreleased main, so build against the staging schema
+          FF_USE_STAGING_SCHEMA: true
         run: pnpm run build
 
       - name: Upload Build