fix: explicitly set machineConfig to null when task machine is removed (#2796)

When a user removes the machine configuration from a task and redeploys, task.machine becomes undefined. Prisma's create() silently skips undefined fields for Json columns rather than setting them to NULL. This change uses the nullish coalescing operator to explicitly pass null, ensuring the machineConfig column is cleared in the database.

Author: deepshekhardas

apps/webapp/app/v3/services/createBackgroundWorker.server.ts

@@ -276,7 +276,7 @@ async function createWorkerTask(
         exportName: task.exportName,
         retryConfig: task.retry,
         queueConfig: task.queue,
-        machineConfig: task.machine,
+        machineConfig: task.machine ?? null,
         triggerSource: task.triggerSource === "schedule" ? "SCHEDULED" : "STANDARD",
         fileId: tasksToBackgroundFiles?.get(task.id) ?? null,
         maxDurationInSeconds: task.maxDuration ? clampMaxDuration(task.maxDuration) : null,