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

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

vllm/model_executor/models/transformers/utils.py

@@ -14,7 +14,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-"""Transformers backend utilities."""
+"""Transformers modeling backend utilities."""
 
 from contextlib import contextmanager
 from pathlib import Path