Show correct extra item in sequence comparison diffs

[SemTiOne]

Sequences of different lengths showed the wrong extra item in the one-liner message. It picked the item at the same index instead of the actual extra one.

E     [1, 2, 3] != [1, 3]
E     test_sequence [1, 3] contains one more item: 3
            != 2

Now it checks whether the tail matches to find the real insertion point.

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• Closes Misleading message "Right contains one more item" #13652
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