Update val.py (#7478)

* Update val.py

is_coco doesn't work!! '/' -> os.sep!!

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* Cleanup

* fix

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

val.py

@@ -155,7 +155,7 @@ def run(
     # Configure
     model.eval()
     cuda = device.type != 'cpu'
-    is_coco = isinstance(data.get('val'), str) and data['val'].endswith('coco/val2017.txt')  # COCO dataset
+    is_coco = isinstance(data.get('val'), str) and data['val'].endswith(f'coco{os.sep}val2017.txt')  # COCO dataset
     nc = 1 if single_cls else int(data['nc'])  # number of classes
     iouv = torch.linspace(0.5, 0.95, 10, device=device)  # iou vector for mAP@0.5:0.95
     niou = iouv.numel()