fix: handle billingSubscriptions gql field if billing is disabled (#9767)

Co-authored-by: etiennejouan <jouan.etienne@gmail.com>

packages/twenty-server/src/engine/core-modules/workspace/workspace.resolver.ts

@@ -167,6 +167,10 @@ export class WorkspaceResolver {
   async billingSubscriptions(
     @Parent() workspace: Workspace,
   ): Promise<BillingSubscription[] | undefined> {
+    if (!this.environmentService.get('IS_BILLING_ENABLED')) {
+      return [];
+    }
+
     try {
       return this.billingSubscriptionRepository.find({
         where: { workspaceId: workspace.id },