Replace deprecated values_of_os() with get_many()

[cakebaker]

This PR replaces the usage of clap's deprecated values_of_os() with get_many().

[niyaznigmatullin]

Seems that tests/misc/chcon-fail.sh fails (https://github.com/uutils/coreutils/runs/7929749317?check_suite_focus=true) because get_many panics

$ ~/repositories/uutils/target/release/coreutils chcon CON
thread 'main' panicked at 'Mismatch between definition and access of `[hash: 9C23C7ACDF5F96F4]`. Could not downcast to TypeId { t: 8720431896296821101 }, need to downcast to TypeId { t: 17148897548463411393 }
', /home/niyaz/repositories/uutils/src/uu/chcon/src/chcon.rs:360:29
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace