docs/backend-system: remove usage of waitForTask in scheduler docs

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

docs/backend-system/core-services/scheduler.md

@@ -134,7 +134,7 @@ Responds with
 
 The `@backstage/backend-test-utils` package provides `mockServices.scheduler`, which provides a mocked implementation of the scheduler service that can be used in tests. This mocked implementation is used by default in `startTestBackend`, and it will immediately run any registered tasks on startup as long as they're not configured to run manually or with an initial delay.
 
-A dedicated instance can be used for more control during testing, with the mock implementation providing additional utilities to trigger and wait for tasks to complete:
+A dedicated instance can be used for more control during testing:
 
 ```ts
 it('should trigger a task', async () => {
@@ -144,16 +144,9 @@ it('should trigger a task', async () => {
     features: [scheduler.factory()],
   });
 
-  // Start waiting for some task to complete
-  const waitForTask = scheduler.waitForTask('some-task-id');
+  await scheduler.triggerTask('some-task-id');
 
-  // Call an endpoit that triggers a task
-  const res = await request(server).post(
-    '/api/my-plugin/route-that-triggers-a-task',
-  );
-  expect(res.status).toBe(200);
-
-  // Wait for the task to complete
-  await waitForTask;
+  // Next verify that the plugin state is updated accordingly
+  // e.g. by calling the API or verifying database state
 });
 ```