leave a FIXME note for --set flags coverage

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

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

@@ -2347,6 +2347,7 @@ impl Config {
                         let current_config_toml = Self::get_toml(config_path);
 
                         // Check the config compatibility
+                        // FIXME: this doesn't cover `--set` flags yet.
                         let res = check_incompatible_options_for_ci_rustc(
                             current_config_toml,
                             ci_config_toml,