Change the way to call legacy functions.

Signed-off-by: Jay Zhang <jiz@microsoft.com>

tests/keras2onnx_unit_tests/conftest.py

@@ -15,10 +15,6 @@
 def is_keras_3():
     return tf.__version__.startswith("2.18") or tf.__version__.startswith("2.17") or tf.__version__.startswith("2.16")
 
-if is_keras_3():
-    import tf_keras
-    K = tf_keras.backend
-
 @pytest.fixture(scope='function')
 def runner():
     np.random.seed(42)
@@ -31,10 +27,15 @@ def runner():
     def runner_func(*args, **kwargs):
         return run_onnx_runtime(*args, model_files, **kwargs)
 
-    # Ensure Keras layer naming is reset for each function
-    K.reset_uids()
-    # Reset the TensorFlow session to avoid resource leaking between tests
-    K.clear_session()
+    if is_keras_3():
+        import tf_keras
+        tf_keras.backend.reset_uids()
+        tf_keras.backend.clear_session()
+    else:
+        # Ensure Keras layer naming is reset for each function
+        K.reset_uids()
+        # Reset the TensorFlow session to avoid resource leaking between tests
+        K.clear_session()
 
     # Provide wrapped run_onnx_runtime function
     yield runner_func