Fix minor logging issue

[curefatih]

Hi

Current usage with the DEBUG mode logs raises errors like this one

File "/usr/local/lib/python3.8/site-packages/nemoguardrails/llm/providers.py", line 55, in discover_langchain_providers
    log.debug("Adding async support to", provider_cls.__name__)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 1434, in debug
    self._log(DEBUG, msg, args, **kwargs)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 1589, in _log
    self.handle(record)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 1599, in handle
    self.callHandlers(record)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 1661, in callHandlers
    hdlr.handle(record)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 954, in handle
    self.emit(record)
  File "/usr/local/lib/python3.8/site-packages/nose/plugins/logcapture.py", line 82, in emit
    self.buffer.append(self.format(record))
  File "/usr/local/lib/python3.8/logging/__init__.py", line 929, in format
    return fmt.format(record)
  File "/usr/local/lib/python3.8/logging/__init__.py", line 668, in format
    record.message = record.getMessage()
  File "/usr/local/lib/python3.8/logging/__init__.py", line 373, in getMessage
    msg = msg % self.args
TypeError: not all arguments converted during string formatting

I believe this is because of the usage of the debug log not including %s. Could you please check? Thanks!