Fix let-env (#3057)

crates/nu-command/src/script.rs

@@ -184,7 +184,7 @@ pub async fn process_script(
         trace!("{:#?}", block);
         let env = ctx.get_env();
 
-        ctx.scope.add_env(env);
+        ctx.scope.add_env_to_base(env);
         let result = run_block(&block, ctx, input_stream).await;
         match result {
             Ok(input) => {