Test: Make doh_unit_test boot_time::timeout_drift less flaky

On cuttlefish, `drift` is sometimes greater than 5ms. This is
probably due to cuttlefish being slow sometimes.

Run the test 200 times on cuttlefish with this change, the
distribution of these 2000 `drift`s is:
  7 out of 2000 over 5ms
  3 out of 2000 over 7ms
  1 out of 2000 over 9ms
  0 out of 2000 over 10ms.

The flaky rate of the test will be less than 0.5% theoretically

Bug: 261906096
Test: run boot_time::timeout_drift 200 times
Change-Id: Ia1c124f58b388357d4b0f96d5c06bce8ab739355