selftests/damon/damon_nr_regions: set ops update for merge results check to 100ms

selftests/damon/damon_nr_regions: set ops update for merge results check to 100ms

damon_nr_regions.py updates max_nr_regions to a number smaller than
expected number of real regions and confirms DAMON respect the harsh
limit.  To give time for DAMON to make changes for the regions, 3
aggregation intervals (300 milliseconds) are given.

The internal mechanism works with not only the max_nr_regions, but also
sz_limit, though.  It avoids merging region if that casn make region of
size larger than sz_limit.  In the test, sz_limit is set too small to
achive the new max_nr_regions, unless it is updated for the new
min_nr_regions.  But the update is done only once per operations set
update interval, which is one second by default.

Hence, the test randomly incurs false positive failures.  Fix it by
setting the ops interval same to aggregation interval, to make sure
sz_limit is updated by the time of the check.

Link: https://lkml.kernel.org/r/20250225222333.505646-3-sj@kernel.org
Fixes: 8bf890c81612 ("selftests/damon/damon_nr_regions: test online-tuned max_nr_regions")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>