tools/unitctl: Update crates

Run 'cargo update' to get the latest version of the required crates in
preparation for the 1.35.0 release.

This resolves a dependabot notification regarding 'crossbeam-channel'.

Link: <https://github.com/nginx/unit/security/dependabot/26>
Signed-off-by: Andrew Clayton <[email protected]>

Author: ac000