Fix test case in test_jagged_tensor.py

[cz171]

Summary: For test_concat, the first values should be from [0:3] given representation

        # f0  []  [1 2] []  [3]
        # f1  [4] [5]   []  [6 7 8]
        # f2  []  []    [9] []

Reviewed By: bigning

Differential Revision: D42521607