val.py assert ncm == nc fix (#8545)

val.py

@@ -164,7 +164,7 @@ def run(
     if not training:
         if pt and not single_cls:  # check --weights are trained on --data
             ncm = model.model.nc
-            assert ncm == nc, f'{weights[0]} ({ncm} classes) trained on different --data than what you passed ({nc} ' \
+            assert ncm == nc, f'{weights} ({ncm} classes) trained on different --data than what you passed ({nc} ' \
                               f'classes). Pass correct combination of --weights and --data that are trained together.'
         model.warmup(imgsz=(1 if pt else batch_size, 3, imgsz, imgsz))  # warmup
         pad = 0.0 if task in ('speed', 'benchmark') else 0.5