test_follow_name_replaced_by_symlink_is_untailable intermittent failure

---- test_tail::test_follow_name_replaced_by_symlink_is_untailable stdout ----
bin: "/Users/runner/work/coreutils/coreutils/target/aarch64-apple-darwin/debug/coreutils"
write(default): /var/folders/8j/sfr9qqcj73j4p6nhwcfpr0th0000gn/T/.tmp7zqhMV/secret
write(default): /var/folders/8j/sfr9qqcj73j4p6nhwcfpr0th0000gn/T/.tmp7zqhMV/watched
run: /Users/runner/work/coreutils/coreutils/target/aarch64-apple-darwin/debug/coreutils tail -F -s.1 --max-unchanged-stats=1 --use-polling watched
remove: /var/folders/8j/sfr9qqcj73j4p6nhwcfpr0th0000gn/T/.tmp7zqhMV/watched
symlink: /var/folders/8j/sfr9qqcj73j4p6nhwcfpr0th0000gn/T/.tmp7zqhMV/secret,/var/folders/8j/sfr9qqcj73j4p6nhwcfpr0th0000gn/T/.tmp7zqhMV/watched

thread 'test_tail::test_follow_name_replaced_by_symlink_is_untailable' panicked at tests/by-util/test_tail.rs:1647:10:
'tail: 'watched' has become inaccessible: No such file or directory
' does not contain 'has been replaced with an untailable symbolic link'
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::stderr_contains
             at ./tests/uutests/src/lib/util.rs:832:9
   3: tests::test_tail::test_follow_name_replaced_by_symlink_is_untailable
             at ./tests/by-util/test_tail.rs:1643:5
   4: tests::test_tail::test_follow_name_replaced_by_symlink_is_untailable::{{closure}}
             at ./tests/by-util/test_tail.rs:1619:56
   5: core::ops::function::FnOnce::call_once
             at /rustc/6b00bc3880198600130e1cf62b8f8a93494488cc/library/core/src/ops/function.rs:250:5
   6: 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/30164209775/job/89694719273?pr=13566

Start with tests/by-util/test_tail.rs around test_tail::test_follow_name_replaced_by_symlink_is_untailable and reproduce the failure using the logged tail -F polling command on macOS. Trace the test's expected stderr and the command result, then confirm the test reliably recognizes the intended untailable-symbolic-link diagnostic.