fixed issue with find not working with symbols that should be escaped (#13792)

# Description

Thanks to @weirdan's suggestion, this now works.

![image](https://github.com/user-attachments/assets/34522c7b-b012-4f73-883d-9913142e85b9)

Closes #13789

crates/nu-command/src/help/help_.rs

@@ -193,7 +193,8 @@ pub fn highlight_search_string(
     string_style: &Style,
     highlight_style: &Style,
 ) -> Result<String, ShellError> {
-    let regex_string = format!("(?i){needle}");
+    let escaped_needle = regex::escape(needle);
+    let regex_string = format!("(?i){escaped_needle}");
     let regex = match Regex::new(&regex_string) {
         Ok(regex) => regex,
         Err(err) => {