docs: add Kylie to deprecated voices list (#897)

Co-authored-by: Vapi Tasker <tasker@vapi.ai>
Co-authored-by: Claude <noreply@anthropic.com>

Author: 3 people

fern/providers/voice/vapi-voices.mdx

@@ -5,7 +5,7 @@ slug: providers/voice/vapi-voices
 ---
 
 <Warning>
-**Legacy Voice Notice:** The following voices are being phased out: **Paige, Spencer, Neha, Harry, Cole, Hana, Lily**
+**Legacy Voice Notice:** The following voices are being phased out: **Paige, Spencer, Neha, Harry, Cole, Hana, Lily, Kylie**
 - Existing assistants using these voices may continue to use them during the transition period
 - New assistants cannot be created using legacy voices
 - Legacy voices will be fully retired in a future update