keras/src/layers/normalization/group_normalization.py/GroupNormalization/_create_broadcast_shape
class GroupNormalization:    def _create_broadcast_shape(self, input_shape):
        broadcast_shape = [1] * len(input_shape)
        broadcast_shape[self.axis] = input_shape[self.axis] // self.groups
        broadcast_shape.insert(self.axis, self.groups)
        return broadcast_shape