fix: use cprintln instead of warn when no tasks are run (#6285)
### Description
The `warn!` macro is meant for logging purposes and prefixes a `WARNING`
to the log message. In order to get identical output as Go we directly
invoke `cprintln` to avoid the prefix.
### Testing Instructions
`EXPERIMENTAL_RUST_CODEPATH=true .cram_env/bin/prysk --shell=bash
tests/filter-run.t` now succeeds
Closes TURBO-1537
Co-authored-by: Chris Olszewski <Chris Olszewski>