tidy: fix bug in rustdoc_json check introduced by rewrite

Author: lolbinarycat

src/tools/tidy/src/rustdoc_json.rs

@@ -17,6 +17,7 @@ pub fn check(src_path: &Path, ci_info: &crate::CiInfo, bad: &mut bool) {
     if crate::files_modified(ci_info, |p| p == RUSTDOC_JSON_TYPES) {
         // `rustdoc-json-types` was not modified so nothing more to check here.
         println!("`rustdoc-json-types` was not modified.");
+        return;
     }
     // Then we check that if `FORMAT_VERSION` was updated, the `Latest feature:` was also updated.
     match crate::git_diff(&base_commit, src_path.join("rustdoc-json-types")) {