test/encoding: disable LeakSanitizer in readable.sh and check-generated.sh

test/encoding: disable LeakSanitizer in readable.sh and check-generated.sh

readable.sh forks two short-lived ceph-dencoder processes per corpus
object(tens of thousands of processes overall). With ASAN's
LeakSanitizer enabled each process runs a whole-heap leak check at exit
that dominates runtime (~10s vs ~1s per process, measured on riscv64).
This test only validates encode/decode behaviour, not leaks, so disable
leak detection while keeping ASAN's other checks active.

check-generated.sh forks ceph-dencoder the same way, so apply the same
fix there.

Signed-off-by: Sun Yuechi <sunyuechi@iscas.ac.cn>