HTTP header casing issue in set comma header function

HTTP header casing issue in set comma header function: a task in harbor-swesmith-rl-artifacts: Harbor SWE-Smith 强化学习数据产物 (Harbor dataset). I'm encountering an issue with the set comma header function in h11. After a recent change, it seems that header casing is not being handled correctly.

The task

I'm encountering an issue with the `set_comma_header` function in h11. After a recent change, it seems that header casing is not being handled correctly.

Part of keryszhan/harbor-swesmith-rl-artifacts.