add non-fixed path option to coco's instances_val2017.json (#11860)

add non-fixed path option fo coco annotations

val.py

@@ -304,6 +304,8 @@ def run(
     if save_json and len(jdict):
         w = Path(weights[0] if isinstance(weights, list) else weights).stem if weights is not None else ''  # weights
         anno_json = str(Path('../datasets/coco/annotations/instances_val2017.json'))  # annotations
+        if not os.path.exists(anno_json):
+            anno_json = os.path.join(data['path'], 'annotations', 'instances_val2017.json')
         pred_json = str(save_dir / f'{w}_predictions.json')  # predictions
         LOGGER.info(f'\nEvaluating pycocotools mAP... saving {pred_json}...')
         with open(pred_json, 'w') as f: