perf test: Use sqrtloop workload to test bperf event

Replace `brstack` workload with `sqrtloop` workload, because `sqrtloop`
workload contains fork(), which is suitable for testing the bperf event
inheritance feature.

Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
Cc: song@kernel.org
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20241021110201.325617-3-wutengda@huaweicloud.com


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