[Docs] Update the name of Transformers backend -> Transformers modeling backend (#28725)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

tests/models/test_transformers.py

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
-"""Test the functionality of the Transformers backend."""
+"""Test the functionality of the Transformers modeling backend."""
 
 from typing import Any
 
@@ -85,7 +85,7 @@ def test_models(
     required = Version("5.0.0.dev")
     if model == "allenai/OLMoE-1B-7B-0924" and installed < required:
         pytest.skip(
-            "MoE models with the Transformers backend require "
+            "MoE models with the Transformers modeling backend require "
             f"transformers>={required}, but got {installed}"
         )