Relax bounds check for throttled driver test

With this commit we relax the check of the lower bound a little bit to
make the test more robust against short system stalls.

tests/driver/driver_test.py

@@ -805,7 +805,7 @@ def test_execute_schedule_throughput_throttled(self, es):
                                  challenges=None)
 
         # in one second (0.5 warmup + 0.5 measurement) we should get 1000 [ops/s] / 4 [clients] = 250 samples
-        for target_throughput, bounds in {10: [2, 4], 100: [24, 26], 1000: [245, 255]}.items():
+        for target_throughput, bounds in {10: [2, 4], 100: [24, 26], 1000: [235, 255]}.items():
             task = track.Task("time-based", track.Operation("time-based", track.OperationType.Bulk.name, params={
                 "body": ["action_metadata_line", "index_line"],
                 "action-metadata-present": True,