Small fix for consistency between C and C++ highlighting. Related to https://github.com/zed-industries/zed/issues/9461 Release Notes: - Change syntax highlighting for preprocessing directive in C so it can be configured with `keyword.directive` instead of being treated as other `keyword`. The behavior should be like the C++ one now. <img width="953" height="343" alt="圖片" src="https://github.com/user-attachments/assets/6b45d2cc-323d-44ba-995f-d77996757669" />