Fix failing test when using man version 2.13.0 (#15123)

The test added in #15115 fails on systems using later versions of `man`
(2.13.0 triggers the issue, at least). This updates the test to ignore
formatting characters.

Thanks to @fdncred and @blindFS for the debugging assistance.

crates/nu-lsp/src/lib.rs

@@ -1025,7 +1025,7 @@ mod tests {
             .to_string();
 
         #[cfg(not(windows))]
-        assert!(hover_text.starts_with("SLEEP(1)"));
+        assert!(hover_text.contains("SLEEP"));
         #[cfg(windows)]
         assert!(hover_text.starts_with("NAME\r\n    Start-Sleep"));
     }