[Fix] Correct parameter in transcription API tutorial

The tutorial was using --static-model-types "transcription" but the
actual implementation requires --static-model-labels "transcription"
for proper routing of transcription requests.

This fixes the documentation mismatch where the tutorial didn't align
with the actual code implementation in the routing logic.

Signed-off-by: David Gao <davidgao313@outlook.com>

Author: davidgao7

tutorials/23-whisper-api-transcription.md

@@ -41,7 +41,7 @@ uv run python3 -m vllm_router.app \
   --service-discovery static \
   --static-backends "$2" \
   --static-models "openai/whisper-small" \
-  --static-model-types "transcription" \
+  --static-model-labels "transcription" \
   --routing-logic roundrobin \
   --log-stats \
   --engine-stats-interval 10 \