Migrate from `collections.Iterable` to `collections.abc.Iterable`.

Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3, and in 3.10 it will stop working.

PiperOrigin-RevId: 454823734
Change-Id: Ic1d22c0badd76c41693967f785f8861746657731

alphafold/model/utils.py

@@ -54,7 +54,7 @@ def mask_mean(mask, value, axis=None, drop_mask_channel=False, eps=1e-10):
     axis = [axis]
   elif axis is None:
     axis = list(range(len(mask_shape)))
-  assert isinstance(axis, collections.Iterable), (
+  assert isinstance(axis, collections.abc.Iterable), (
       'axis needs to be either an iterable, integer or "None"')
 
   broadcast_factor = 1.