Fix potential ReDoS by escaping tokenizer filename used as regex pattern (#47498)
* Fix potential ReDoS by escaping tokenizer filename used as regex pattern
vocab_files["tokenizer_file"] originates from the model repository's
tokenizer_config.json but was passed to re.search() as the regex pattern,
so a repository-controlled filename could inject regex metacharacters and
trigger catastrophic backtracking during from_pretrained. Wrap it in
re.escape() to match the literal filename; behaviour is unchanged for
normal filenames.
* Fix replaced re with a plain not in check