TFLite --int8 'flatbuffers==1.12' fix (ultralytics#6216)

* TFLite `--int8` 'flatbuffers==1.12' fix

Temporary workaround for TFLite INT8 export.

* Update export.py

* Update export.py

Author: glenn-jocher

export.py

@@ -277,8 +277,6 @@ def export_tflite(keras_model, im, file, int8, data, ncalib, prefix=colorstr('Te
     try:
         import tensorflow as tf
 
-        from models.tf import representative_dataset_gen
-
         LOGGER.info(f'\n{prefix} starting export with tensorflow {tf.__version__}...')
         batch_size, ch, *imgsz = list(im.shape)  # BCHW
         f = str(file).replace('.pt', '-fp16.tflite')
@@ -288,6 +286,8 @@ def export_tflite(keras_model, im, file, int8, data, ncalib, prefix=colorstr('Te
         converter.target_spec.supported_types = [tf.float16]
         converter.optimizations = [tf.lite.Optimize.DEFAULT]
         if int8:
+            from models.tf import representative_dataset_gen
+            check_requirements(('flatbuffers==1.12',))  # https://github.com/ultralytics/yolov5/issues/5707
             dataset = LoadImages(check_dataset(data)['train'], img_size=imgsz, auto=False)  # representative data
             converter.representative_dataset = lambda: representative_dataset_gen(dataset, ncalib)
             converter.target_spec.supported_ops = [tf.lite.OpsSet.TFLITE_BUILTINS_INT8]