Replace print() with logging.info() in trainloader (ultralytics#3103)

Might indirectly help ultralytics#3095 by providing better visibility on source of corruption.

utils/datasets.py

@@ -490,14 +490,14 @@ def cache_labels(self, path=Path('./labels.cache'), prefix=''):
                 x[im_file] = [l, shape, segments]
             except Exception as e:
                 nc += 1
-                print(f'{prefix}WARNING: Ignoring corrupted image and/or label {im_file}: {e}')
+                logging.info(f'{prefix}WARNING: Ignoring corrupted image and/or label {im_file}: {e}')
 
             pbar.desc = f"{prefix}Scanning '{path.parent / path.stem}' images and labels... " \
                         f"{nf} found, {nm} missing, {ne} empty, {nc} corrupted"
         pbar.close()
 
         if nf == 0:
-            print(f'{prefix}WARNING: No labels found in {path}. See {help_url}')
+            logging.info(f'{prefix}WARNING: No labels found in {path}. See {help_url}')
 
         x['hash'] = get_hash(self.label_files + self.img_files)
         x['results'] = nf, nm, ne, nc, i + 1