uucore - test_tty_from fails.

[plugwash]

We recently updated the uucore crate in Debian, and I was looking through the test failures. Most of them seem related to our test environment, but this one did not seem in any way environment specific.

thread 'features::tty::tests::test_tty_from' panicked at src/lib/features/tty.rs:101:44:
called `Result::unwrap()` on an `Err` value: ()

assert_eq!(Teletype::try_from("?").unwrap(), Teletype::Unknown);

When I look at the code for Teletype::try_from, I see that the impl for "String" has a special case for "?" but the impl for "&str" has no such special case. Such an inconsistency seems wrong, and this also suggests that noone ever actually ran the tests in question.