create a better error message when saving fails (#13290)

# Description

This PR just creates a better error message when the `save` command
fails.

# User-Facing Changes
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crates/nu-command/src/filesystem/save.rs

@@ -461,7 +461,7 @@ fn open_file(path: &Path, span: Span, append: bool) -> Result<File, ShellError>
     };
 
     file.map_err(|e| ShellError::GenericError {
-        error: "Permission denied".into(),
+        error: format!("Problem with [{}], Permission denied", path.display()),
         msg: e.to_string(),
         span: Some(span),
         help: None,