Fix bug with unknown node type (#13406)

tools/pot/tests/data/models/split_concat_example/split_concat_example.json

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:a92b39ec5936e038627cae4e3a080322aba4785f181fd3493d83d56014cc1c0c
+size 172

tools/pot/tests/data/models/split_concat_example/split_concat_example.onnx

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6e6b221ddce1eb1536ba7e5c3112e137dde45181e314ab436da5ff4fb236c9b6
+size 449

tools/pot/tests/data/reference_models/split_concat_example_pytorch.xml

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:46ed853f0550eb2be4f8c48257c070aa98f8f811de7764e78074130f89f96f6b
+size 8751

tools/pot/tests/test_graph.py

@@ -30,6 +30,7 @@ TEST_MODELS = [
     ('resnet_example', 'pytorch', 'CPU_SPR'),
     #('tensor_iterator_example', 'tf', 'ANY'),
     ('softsign_example', 'tf', 'GNA'),
+    ('split_concat_example', 'pytorch', 'ANY'),
 ]