sort: ignore broken pipes in a test

Since sort exits early due to the nonexistent file, it might no longer
be around when we try to send it the input.
This is "by design" and can be ignored.

tests/by-util/test_sort.rs

@@ -1000,6 +1000,7 @@ fn test_verifies_out_file() {
         new_ucmd!()
             .args(&["-o", "nonexistent_dir/nonexistent_file"])
             .pipe_in(input)
+            .ignore_stdin_write_error()
             .fails()
             .status_code(2)
             .stderr_only(