test(cli): a child that exits before draining stdin breaks the write, not the test

The FreeBSD run of run_reads_commands_from_a_file_or_stdin hit a race: the CLI
exits with code 2 on the usage-error cases before the helper finishes writing
its standard input, so write_all fails with BrokenPipe and the unwrap panicked
at apps/effectcraft-cli/tests/it/cli.rs:139:61.

Ignore exactly BrokenPipe while writing the piped standard input and assert on
any other error kind, so an early exit keeps feeding the assertions below
instead of failing the harness.

Fixes #2794

Co-authored-by: rahul05ranjan <11793455+rahul05ranjan@users.noreply.github.com>

apps/effectcraft-cli/tests/it/cli.rs

@@ -136,7 +136,14 @@ fn run_reads_arguments_from_a_file() {
 /// Run with `stdin` piped in; returns (exit code, stdout, stderr).
 fn run_with_stdin(args: &[&str], stdin: &str) -> (i32, String, String) {
     let mut child = bin().args(args).stdin(Stdio::piped()).stdout(Stdio::piped()).stderr(Stdio::piped()).spawn().unwrap();
-    child.stdin.take().unwrap().write_all(stdin.as_bytes()).unwrap();
+    // The child may exit before it has read all of standard input (the usage-error cases below
+    // exit with code 2 without draining stdin), so a broken pipe while writing is that early
+    // exit, not a failure of this helper; the assertions on the returned output still hold.
+    let mut stdin_pipe = child.stdin.take().unwrap();
+    if let Err(err) = stdin_pipe.write_all(stdin.as_bytes()) {
+        assert_eq!(err.kind(), std::io::ErrorKind::BrokenPipe, "writing the child's standard input: {err}");
+    }
+    drop(stdin_pipe);
     let out = child.wait_with_output().unwrap();
     (out.status.code().unwrap_or(-1), String::from_utf8_lossy(&out.stdout).into_owned(), String::from_utf8_lossy(&out.stderr).into_owned())
 }