ci: try to reproduce spurious stdin timeout

[mkroening]

This PR tries to reproduce the following spurious stdin timeout:

$ cargo xtask ci rs --arch aarch64 --profile release --features hermit/semihosting --package stdin qemu
[...]
[    0.028809][0][INFO  hermit    ] Jumping into application
[    0.029054][0][WARN  entropy   ] Unable to read entropy! Fallback to a naive implementation!
Hello, there!
Hello, there!
Hello, again!
Hello, again!
Bye-by

thread 'main' (9854) panicked at xtask/src/ci/qemu.rs:542:9:
assertion failed: stdout_lines.iter().any(|line| line.contains(message))
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace