fishaudio/Bert-VITS2 Command Injection in webui_preprocess.py bert_gen function

Bert-VITS2 is the VITS2 Backbone with multilingual bert. User input supplied to the data_dir variable is used directly in a command executed with subprocess.run(cmd, shell=True) in the bert_gen function, which leads to arbitrary command execution. This affects fishaudio/Bert-VITS2 2.3 and earlier.