Fix Event::kind serialization with serialization-compat-6

[Legend-Master]

The kind field in Event was serialized as type in v6, but is kind with serialization-compat-6 feature

Reference: tauri-apps/plugins-workspace#2221

I'm not sure how the release process work here, let me know if I need to add a change log entry (if so please also tell me what version should this change be in, since I see there's already a notify-types 2.0.0 (unreleased) entry) or do I need to target another branch

[dfaust]

Thank you for the fix.
I'll merge it into main and create a new branch based on the last tag and then cherry-pick this commit.