Update build.py

there was a change in Python 3.10 and the Mapping class has been moved to the collections.abc module. So, if you're using Python 3.10 or later, you should import the Mapping class from the collections.abc module, not the collections module

fastreid/data/build.py

@@ -16,7 +16,7 @@ if TORCH_MAJOR == 1 and TORCH_MINOR < 8:
 else:
     string_classes = str
 
-from collections import Mapping
+from collections.abc import Mapping
 
 from fastreid.config import configurable
 from fastreid.utils import comm