tests: cleanup tests/ui/command/command-setgroups.rs

- Use `only-unix` instead of `ignore-windows`.
- Replace `ignore-*` with `needs-subprocess`.

Author: jieyouxu

tests/ui/command/command-setgroups.rs

@@ -1,9 +1,8 @@
 //@ run-pass
-//@ ignore-windows - this is a unix-specific test
-//@ ignore-wasm32
-//@ ignore-sgx
+//@ only-unix (this is a unix-specific test)
 //@ ignore-musl - returns dummy result for _SC_NGROUPS_MAX
 //@ ignore-nto - does not have `/bin/id`, expects groups to be i32 (not u32)
+//@ needs-subprocess
 
 #![feature(rustc_private)]
 #![feature(setgroups)]