Don't expanding globs if user pass variables. (#11946)

# Description
Fixes: #11912

# User-Facing Changes
After this change: 
```
let x = '*.nu'; ^echo $x
```
will no longer expand glob.
If users still want to expand glob, there are also 3 ways to do this:
```
# 1. use spread operation with `glob` command
let x = '*.nu'; ^echo ...(glob $x)
```
# Tests + Formatting
Done

# After Submitting
NaN

tests/shell/pipeline/commands/external.rs

@@ -1,4 +1,6 @@
+use nu_test_support::fs::Stub::EmptyFile;
 use nu_test_support::nu;
+use nu_test_support::playground::Playground;
 use pretty_assertions::assert_eq;
 
 #[cfg(feature = "which-support")]
@@ -166,6 +168,35 @@ fn err_pipe_with_failed_external_works() {
     assert_eq!(actual.out, "4");
 }
 
+#[test]
+fn dont_run_glob_if_pass_variable_to_external() {
+    Playground::setup("dont_run_glob", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("jt_likes_cake.txt"),
+            EmptyFile("andres_likes_arepas.txt"),
+        ]);
+
+        let actual = nu!(cwd: dirs.test(), r#"let f = "*.txt"; nu --testbin nonu $f"#);
+
+        assert_eq!(actual.out, "*.txt");
+    })
+}
+
+#[test]
+fn run_glob_if_pass_variable_to_external() {
+    Playground::setup("run_glob_on_external", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("jt_likes_cake.txt"),
+            EmptyFile("andres_likes_arepas.txt"),
+        ]);
+
+        let actual = nu!(cwd: dirs.test(), r#"let f = "*.txt"; nu --testbin nonu ...(glob $f)"#);
+
+        assert!(actual.out.contains("jt_likes_cake.txt"));
+        assert!(actual.out.contains("andres_likes_arepas.txt"));
+    })
+}
+
 mod it_evaluation {
     use super::nu;
     use nu_test_support::fs::Stub::{EmptyFile, FileWithContent, FileWithContentToBeTrimmed};