test_cp: On MacOS, ignore tests that use /dev/fd/0

For unclear reason, this is a source of test flakiness (#8453).

Author: drinkcat

tests/by-util/test_cp.rs

@@ -6322,6 +6322,7 @@ fn test_cp_archive_preserves_directory_permissions() {
 
 #[test]
 #[cfg(unix)]
+#[cfg_attr(target_os = "macos", ignore = "Flaky on MacOS, see #8453")]
 fn test_cp_from_stdin() {
     let (at, mut ucmd) = at_and_ucmd!();
     let target = "target";
@@ -6389,6 +6390,7 @@ fn test_cp_update_none_interactive_prompt_no() {
 
 /// only unix has `/dev/fd/0`
 #[cfg(unix)]
+#[cfg_attr(target_os = "macos", ignore = "Flaky on MacOS, see #8453")]
 #[test]
 fn test_cp_from_stream() {
     let target = "target";
@@ -6415,6 +6417,7 @@ fn test_cp_from_stream() {
 
 /// only unix has `/dev/fd/0`
 #[cfg(unix)]
+#[cfg_attr(target_os = "macos", ignore = "Flaky on MacOS, see #8453")]
 #[test]
 fn test_cp_from_stream_permission() {
     let target = "target";