[CI Problem] Flaky test `test_task_scheduler_gradient`

[masahi]

https://ci.tlcpack.ai/blue/organizations/jenkins/tvm/detail/PR-10351/1/pipeline

I definitely saw that multiple times recently.

[zxybazh]

I think it's a floating point issue because the 1st gradient is too close to 0 and the autoscheduler would randomly pick a task in that case. Changing the objective_func to 1e5 * costs[0] can fix the test.