test(agent): add a fail case test for postprocess (TabbyML#1294)

* test(agent): add a fail case test for postprocess

* fix extension name

* Update clients/tabby-agent/src/postprocess/golden/remove_duplication/duplicated_line_suffix.toml

Co-authored-by: Zhiming Ma <codes.icy@gmail.com>

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Co-authored-by: Zhiming Ma <codes.icy@gmail.com>