selftests: cgroup: fix unexpected failure on test_memcg_low

selftests: cgroup: fix unexpected failure on test_memcg_low

[ Upstream commit 19ab365762c6cc39dfdee9e13ab0d12fe4b5540d ]

Since commit f079a020ba95 ("selftests: memcg: factor out common parts of
memory.{low,min} tests"), the value used in second alloc_anon has changed
from 148M to 170M.  Because memory.low allows reclaiming page cache in
child cgroups, so the memory.current is close to 30M instead of 50M.
Therefore, adjust the expected value of parent cgroup.

Link: https://lkml.kernel.org/r/20230522095233.4246-2-haifeng.xu@shopee.com
Fixes: f079a020ba95 ("selftests: memcg: factor out common parts of memory.{low,min} tests")
Signed-off-by: Haifeng Xu <haifeng.xu@shopee.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>