fix ls_colors coloring in grid and ls (#13935)

# Description

After PR https://github.com/nushell/nushell/pull/12953, LS_COLORS
coloring broke in the `grid` and `ls` commands because the full path to
the files were not available. This PR restores the coloring.


# User-Facing Changes
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crates/nu-command/src/system/run_external.rs

@@ -623,8 +623,16 @@ mod test {
 
     #[test]
     fn test_write_pipeline_data() {
-        let engine_state = EngineState::new();
+        let mut engine_state = EngineState::new();
         let stack = Stack::new();
+        let cwd = std::env::current_dir()
+            .unwrap()
+            .into_os_string()
+            .into_string()
+            .unwrap();
+
+        // set the PWD environment variable as it's required now
+        engine_state.add_env_var("PWD".into(), Value::string(cwd, Span::test_data()));
 
         let mut buf = vec![];
         let input = PipelineData::Empty;