Update data.uint8 to GetTensorData<int8_t> in micro_allocator_test.cc 
Update data.uint8 to GetTensorData<int8_t> in micro_allocator_test.cc 

Changed all instances of data.uint8 to use GetTensorData<int8_t>, since all tensors are int8 quantized.
BUG=[b/207417110](https://buganizer.corp.google.com/issues/207417110)
tensorflow/tflite-micro,tensorflow/tflite-micro,tensorflow/tflite-micro,tensorflow/tflite-micro