test: Use a larger default term width

[Muscraft]

@ehuss made a comment saying that cargo should set __CARGO_TEST_TTY_WIDTH_DO_NOT_USE_THIS to a very large value to avoid problems with long paths in tests. This PR does that by setting it to 200 (the previous default was 140).

Note: 200 is a start, and we can always go up if needed

[rustbot]

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