generate-test runner prone to OOM

[JonathanFoo0523]

Out of memory: Killed process 1038168 (python3) total-vm:63961176kB, anon-rss:63494512kB, file-rss:768kB, shmem-rss:0kB, UID:1000 pgtables:124416kB oom_score_adj:0

run with
32 vCPU, and 32 max parallel task