Make Semicolon stop on error (#6079)

* introduce external command runs to failed error, and implement semicolon relative logic

* ignore test due to semicolon works

* not raise ShellError for external commands

* update comment

* add relative test in for windows

* fix type-o

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

crates/nu-command/src/env/let_env.rs

@@ -43,6 +43,7 @@ impl Command for LetEnv {
 
         let rhs =
             eval_expression_with_input(engine_state, stack, keyword_expr, input, false, true)?
+                .0
                 .into_value(call.head);
 
         if env_var == "PWD" {