fix: gate cmux test to macos (linux has no cmux preset)

Author: aannoo

src/commands/config.rs

@@ -1695,6 +1695,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(target_os = "macos")]
     fn test_terminal_help_text_lists_cmux_as_managed() {
         crate::config::Config::reset();
         crate::config::Config::init();