whoami: fix usage line for unexpected arguments

[YuF-9468]

Summary

• fix whoami clap usage override to use a localized key instead of util name
• add whoami-usage = whoami in en-US and fr-FR locale files

Fixes #11155

Testing

• Could not run local Rust checks in this environment because cargo is not installed.
• Change mirrors the existing accepted pattern used in similar utils (e.g. logname).

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/resolution (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/symlink (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/misc/io-errors is no longer failing!
Congrats! The gnu test tests/timeout/timeout-group is no longer failing!
Congrats! The gnu test tests/tail/tail-n0f is now passing!

[oech3]

Please install cargo.

[cakebaker]

Thanks for your PR!