fix: adds thread-ts to slack event (#723)

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Author: jayhack

src/codegen/extensions/slack/types.py

@@ -30,6 +30,7 @@ class SlackEvent(BaseModel):
     blocks: list[Block] | None = None
     channel: str
     event_ts: str
+    thread_ts: str | None = None
 
 
 class SlackWebhookPayload(BaseModel):