Fixes a flake where the following can happen:

• A build starts at 23:34:59.981 but ends at 23:35:00.205
• When calculating the deadline of 1 hour we set on the build we get 00:35:00.205.
• We pass a tick that adds 61 minutes but it's based off the created_at instead of the completed_at of the build so we get 00:35:59.981 which truncates down to 00:35:00 which is less than the deadline.

I've gone ahead and fixed it but we should maybe reconsider whether this test should exist in autobuild since it's really testing that the deadline is set correctly in provisionerdserver. We can't really refactor this test with dbfake without completely obviating what it's trying to test.

fixes #10359