perf test: Use cycles event in perf record test for leader_sampling

On s390 the event instructions can not be used for recording.
This event is only supported by perf stat.

Change the event from instructions to cycles in subtest
test_leader_sampling.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Suggested-by: James Clark <james.clark@linaro.org>
Reviewed-by: James Clark <james.clark@linaro.org>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/r/20250131102756.4185235-3-tmricht@linux.ibm.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>