make first behave same way as last: always return list when with number argument (#6616)

* make `first` behave same way as `last`

* better behaviour

* fix tests

* add tests

tests/shell/pipeline/commands/external.rs

@@ -232,7 +232,7 @@ mod stdin_evaluation {
                 | nu --testbin chop
                 | nu --testbin chop
                 | lines
-                | first 1 )
+                | first )
             "#
         ))
         .out;