Spurious failure of shell_is_not_executable test

[bjorn3]

While sudo-rs correctly returns a non-zero exit code, sometimes on CI it seems like it fails to write the error message to stderr. I haven't been able to reproduce locally.

---- sudo::flag_shell::shell_is_not_executable stdout ----
thread 'sudo::flag_shell::shell_is_not_executable' panicked at sudo-compliance-tests/src/sudo/flag_shell.rs:228:9:
"" did not contain "Permission denied"
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

An example of a failure is https://github.com/trifectatechfoundation/sudo-rs/actions/runs/13265821777/job/37032919490?pr=991