PYSEC-2021-410

TensorFlow is an open source platform for machine learning. In affected versions the shape inference code for AllToAll can be made to execute a division by 0. This occurs whenever the split_count argument is 0. The fix will be included in TensorFlow 2.7.0. We will also cherrypick this commit on TensorFlow 2.6.1, TensorFlow 2.5.2, and TensorFlow 2.4.4, as these are also affected and still in supported range.