update allowed extra checks for tidy

Author: klensy

src/bootstrap/src/core/config/flags.rs

@@ -382,7 +382,7 @@ pub enum Subcommand {
         bless: bool,
         #[arg(long)]
         /// comma-separated list of other files types to check (accepts py, py:lint,
-        /// py:fmt, shell)
+        /// py:fmt, shell, shell:lint, cpp, cpp:fmt, spellcheck, spellcheck:fix)
         extra_checks: Option<String>,
         #[arg(long)]
         /// rerun tests even if the inputs are unchanged