test_cat_broken_pipe_nonzero_and_message intermittent failure

---- test_cat::test_cat_broken_pipe_nonzero_and_message stdout ----
bin: "/Users/runner/work/coreutils/coreutils/target/x86_64-apple-darwin/debug/coreutils"
run: /Users/runner/work/coreutils/coreutils/target/x86_64-apple-darwin/debug/coreutils cat

thread 'test_cat::test_cat_broken_pipe_nonzero_and_message' panicked at tests/by-util/test_cat.rs:36:10:
Command was expected to fail.
stdout = 
 stderr = 
stack backtrace:
   0: __rustc::rust_begin_unwind
             at /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/library/std/src/panicking.rs:697:5
   1: core::panicking::panic_fmt
             at /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/library/core/src/panicking.rs:75:14
   2: uutests::util::CmdResult::failure
             at ./tests/uutests/src/lib/util.rs:478:9
   3: uutests::util::UCommand::fails
             at ./tests/uutests/src/lib/util.rs:2073:9
   4: tests::test_cat::test_cat_broken_pipe_nonzero_and_message
             at ./tests/by-util/test_cat.rs:33:5
   5: tests::test_cat::test_cat_broken_pipe_nonzero_and_message::{{closure}}
             at ./tests/by-util/test_cat.rs:24:46
   6: core::ops::function::FnOnce::call_once
             at /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/library/core/src/ops/function.rs:250:5
   7: core::ops::function::FnOnce::call_once
             at /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

https://github.com/uutils/coreutils/actions/runs/25024061697/job/73291581399?pr=12047

Start with tests/by-util/test_cat.rs, especially test_cat_broken_pipe_nonzero_and_message around lines 24-36, and reproduce the test on the macOS target shown in the CI log. Trace the broken-pipe command setup and its expected failure and message. Done means the intermittent test reliably observes the intended nonzero status and diagnostic without masking other failures.