Small fix for PostProcessing test

tests/test_PostProcessing.py

@@ -168,7 +168,7 @@ def test_plot_metamodel_3d_nopce(basic_engine) -> None:
     post = PostProcessing(engine)
     with pytest.raises(AttributeError) as excinfo:
         post.plot_metamodel_3d()
-    assert str(excinfo.value) == 'This evaluation only support PCE-type models!'
+    assert str(excinfo.value) == 'This function is only applicable if the MetaModel input dimension is 2.'
     
 
 #%% _get_sample