tiflash: correct the default value of task_scheduler_active_set_soft_limit (#20474)#20484

ti-chi-bot[bot] merged 6 commits intopingcap:release-8.5pingcap/docs-cn:release-8.5from

ti-chi-bot:cherry-pick-20474-to-release-8.5ti-chi-bot/docs-cn:cherry-pick-20474-to-release-8.5Copy head branch name to clipboard