text: Title: Fix `get_stacktrace`
  Body: ### Summary
  
  The result of `traceback.format_exception` already includes newlines. We don't need add it.
  
  ```diff
  diff --git a/mlflow/utils/exception_utils.py b/mlflow/utils/exception_utils.py
  index a73f266c3..8f73853db 100644
  --- a/mlflow/utils/exception_utils.py
  +++ b/mlflow/utils/exception_utils.py
  @@ -9,6 +9,6 @@ def get_stacktrace(error):
               tb = traceback.format_exception(error.__class__, error, error.__traceback__)
           else:
               tb = traceback.format_exception(error)
  -        return (msg + "\n\n".join(tb)).strip()
  +        return (msg + "".join(tb)).strip()
       except Exception:
           return msg
  ```
  
  The message generated by this function currently looks like this:
  
  ```
  AttributeError("'list' object has no attribute 'columns'")Traceback (most recent call last):
  
  
    File "/Users/harutaka.kawamura/Desktop/repositories/mlflow/mlflow/utils/_capture_modules.py", line 166, in load_model_and_predict
      model.predict(input_example, params=params)
  
  
    File "/Users/harutaka.kawamura/Desktop/repositories/mlflow/mlflow/openai/__init__.py", line 785, in predict
      return self._predict_chat(data, params or {})
  
  
    File "/Users/harutaka.kawamura/Desktop/repositories/mlflow/mlflow/openai/__init__.py", line 703, in _predict_chat
      messages_list = self.format_completions(self.get_params_list(data))
  
  
    File "/Users/harutaka.kawamura/Desktop/repositories/mlflow/mlflow/openai/__init__.py", line 665, in get_params_list
      if variable in data.columns:
  ```
  
  but it should look like:
  
  ```
  AttributeError("'list' object has no attribute 'columns'")
  Traceback (most recent call last):
    File "/Users/harutaka.kawamura/Desktop/repositories/mlflow/mlflow/utils/_capture_modules.py", line 166, in load_model_and_predict
      model.predict(input_example, params=params)
    File "/Users/harutaka.kawamura/Desktop/repositories/mlflow/mlflow/openai/__init__.py", line 785, in predict
      return self._predict_chat(data, params or {})
    File "/Users/harutaka.kawamura/Desktop/repositories/mlflow/mlflow/openai/__init__.py", line 703, in _predict_chat
      messages_list = self.format_completions(self.get_params_list(data))
    File "/Users/harutaka.kawamura/Desktop/repositories/mlflow/mlflow/openai/__init__.py", line 665, in get_params_list
      if variable in data.columns:
  ```
  
  ### Notes
  
  - Make sure to open a PR from a **non-master** branch.
  - Sign off the commit using the `-s` flag when making a commit:
  
    ```sh
    git commit -s -m "..."
             # ^^ make sure to use this
    ```
  
  - Include `#{issue_number}` (e.g. `#123`) in the PR description when opening a PR.
  