Update Objects365.yaml (ultralytics#7323)

Updated dataset size to 712GB (includes undeleted zips).

data/Objects365.yaml

@@ -4,7 +4,7 @@
 # parent
 # ├── yolov5
 # └── datasets
-#     └── Objects365  ← downloads here (750 GB)
+#     └── Objects365  ← downloads here (712 GB)
 
 
 # Train/val/test sets as 1) dir: path/to/imgs, 2) file: path/to/imgs.txt, or 3) list: [path/to/imgs1, path/to/imgs2, ..]