CI is too slow

CI used to take ~5 mins total, but is now commonly taking over 30 mins. This is extremely limiting, especially now we have enabled merge queue. Items often spend an hour or more in the queue, and can then drop out due to flakiness.

Investigate which CI jobs are the slowest and why, and find fixes.

首先检查最近的 CI 运行并比较每个 job 的耗时。调查最慢的 job 和报告的 flakiness，然后验证提议的修复是否能减少 CI 总耗时，并防止项目从 merge queue 中掉出。

由索引模型根据 Issue 内容生成。