message: Add missing colocated element in test in buffer_assignment_test.
  This was resulting in a flaky test because sometimes the live set would include this missing colocated element perhaps because the buffers in the allocation has some nondeterministic order (read from a map?).
diff: @@ -1634,6 +1634,7 @@ TEST_F(BufferAssignmentTest, PeakBuffersWhile) {
  }
  EXPECT_EQ(bcast_buffer->instruction(), bcast);
  EXPECT_TRUE(
  + nonbcast_buffer->instruction() == copy ||
  nonbcast_buffer->instruction() == while_op ||
  nonbcast_buffer->instruction() == body->parameter_instruction(0) ||
  nonbcast_buffer->instruction() == body->root_instruction() ||
  