make stderr works for failed external command (#11914)

# Description
Fixes: #11913

When running external command, nushell shouldn't consumes stderr
messages, if user want to redirect stderr.

# User-Facing Changes
NaN

# Tests + Formatting
Done

# After Submitting
NaN

src/main.rs

@@ -269,6 +269,7 @@ fn main() -> Result<()> {
         match testbin.item.as_str() {
             "echo_env" => test_bins::echo_env(true),
             "echo_env_stderr" => test_bins::echo_env(false),
+            "echo_env_stderr_fail" => test_bins::echo_env_and_fail(false),
             "echo_env_mixed" => test_bins::echo_env_mixed(),
             "cococo" => test_bins::cococo(),
             "meow" => test_bins::meow(),

src/test_bins.rs

@@ -16,6 +16,11 @@ pub fn echo_env(to_stdout: bool) {
     }
 }
 
+pub fn echo_env_and_fail(to_stdout: bool) {
+    echo_env(to_stdout);
+    fail();
+}
+
 fn echo_one_env(arg: &str, to_stdout: bool) {
     if let Ok(v) = std::env::var(arg) {
         if to_stdout {