[Minor] Enhance error message for TRTLLM decode uniformity check (#36609)

Signed-off-by: Woosuk Kwon <woosuk@inferact.ai>

vllm/v1/attention/backends/flashinfer.py

@@ -1111,6 +1111,7 @@ class FlashInferMetadataBuilder(AttentionMetadataBuilder[FlashInferMetadata]):
             if decode_use_trtllm:
                 assert num_decode_tokens % num_decodes == 0, (
                     "TRTLLM decode requires uniform query lengths per request. "
+                    f"Got {num_decode_tokens=} and {num_decodes=}."
                 )
                 attn_metadata.decode = TRTLLMDecode(
                     block_tables=block_table_tensor[:num_decodes],