numfmt: numfmt --debug 2>/dev/full does not abort

[tuananh]

Fixes: #10658

[tuananh]

 failures:

---- test_dd::test_stdin_stdout_skip stdout ----
bin: "/home/runner/work/coreutils/coreutils/target/x86_64-unknown-linux-gnu/debug/coreutils"
run: /home/runner/work/coreutils/coreutils/target/x86_64-unknown-linux-gnu/debug/coreutils dd status=none skip=2 ibs=128

thread 'test_dd::test_stdin_stdout_skip' panicked at tests/uutests/src/lib/util.rs:412:35:
called `Option::unwrap()` on a `None` value
stack backtrace:
   0: rust_begin_unwind
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/std/src/panicking.rs:692:5
   1: core::panicking::panic_fmt
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/panicking.rs:75:14
   2: core::panicking::panic
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/panicking.rs:145:5
   3: core::option::unwrap_failed
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/option.rs:2015:5
   4: core::option::Option<T>::unwrap
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/option.rs:978:21
   5: uutests::util::CmdResult::code
             at ./tests/uutests/src/lib/util.rs:412:9
   6: uutests::util::CmdResult::success
             at ./tests/uutests/src/lib/util.rs:456:13
   7: uutests::util::UCommand::succeeds
             at ./tests/uutests/src/lib/util.rs:1996:9
   8: tests::test_dd::test_stdin_stdout_skip
             at ./tests/by-util/test_dd.rs:159:5
   9: tests::test_dd::test_stdin_stdout_skip::{{closure}}
             at ./tests/by-util/test_dd.rs:155:28
  10: core::ops::function::FnOnce::call_once
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/ops/function.rs:250:5
  11: core::ops::function::FnOnce::call_once
             at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.


failures:
    test_dd::test_stdin_stdout_skip

the failed test looks unrelated with this :-/