message: Fixing reduceScatterwithinReplica doc string
  Summary: Adding missing arg to docs string.
  Test Plan: CI
  Reviewers: #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, georgep
  Maniphest Tasks: T51795
diff: @@ -75,9 +75,9 @@ def reduce_scatter(input_shards, op):
  IPU3 [x3, y3, z3]
  Output: IPU0 [0]
  - IPU1 [op(y0, y1, y2)]
  - IPU2 [op(z0, z1, z2)]
  - IPU3 [op(x0, x1, x2)]
  + IPU1 [op(y0, y1, y2, y3)]
  + IPU2 [op(z0, z1, z2, z3)]
  + IPU3 [op(x0, x1, x2, x3)]
  Args:
  input_shards: The tensors to reduce. These are expected to be supplied in
  