test/crimson/seastore/CMakeLists: tune ASan's UAR fake stack size

test/crimson/seastore/CMakeLists: tune ASan's UAR fake stack size

Avoids severe slowdowns with detect_stack_use_after_return=1.
The root cause is unclear, but ASan's fake stack GC behavior is
suspected. Tuning the UAR (Use-After-Return) fake stack size
(reduced from 64KB–1MB to 64KB) helped delay the onset of the
performance degradation.

Fixes: https://tracker.ceph.com/issues/71704
Signed-off-by: Chanyoung Park <chaney.p@kakaoenterprise.com>