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>

Author: Tengda Wu

tools/perf/tests/shell/stat_bpf_counters.sh

@@ -4,7 +4,7 @@
 
 set -e
 
-workload="perf test -w brstack"
+workload="perf test -w sqrtloop"
 
 # check whether $2 is within +/- 20% of $1
 compare_number()