DOC: fix EX03 Errors for pandas.DataFrame.to_sql
- [X] Ref: https://github.com/pandas-dev/pandas/issues/56804

Fix these EX03 Errors for `pandas.DataFrame.to_sql`:

```
9 Errors found for `pandas.DataFrame.to_sql`:
        flake8 error: line 8, col 4: E111 indentation is not a multiple of 4
        flake8 error: line 15, col 4: E111 indentation is not a multiple of 4
        flake8 error: line 19, col 4: E111 indentation is not a multiple of 4
        flake8 error: line 27, col 1: F821 undefined name 'df_conflict'
        flake8 error: line 27, col 89: E501 line too long (124 > 88 characters)
        flake8 error: line 28, col 1: F811 redefinition of unused 'insert' from line 22
        flake8 error: line 39, col 1: F821 undefined name 'df_conflict'
        flake8 error: line 39, col 89: E501 line too long (123 > 88 characters)
        flake8 error: line 46, col 3: E111 indentation is not a multiple of 4
```
@erichxchen, thank you for working on this. I think, there are some errors left that need to be fixed:
```
5 Errors found for `pandas.DataFrame.to_sql`:
        EX03    flake8 error: line 27, col 1: F821 undefined name 'df_conflict'
        EX03    flake8 error: line 27, col 89: E501 line too long (124 > 88 characters)
        EX03    flake8 error: line 28, col 1: F811 redefinition of unused 'insert' from line 22
        EX03    flake8 error: line 39, col 1: F821 undefined name 'df_conflict'
        EX03    flake8 error: line 39, col 89: E501 line too long (123 > 88 characters)
```
For example, the line 
https://github.com/pandas-dev/pandas/blob/02011f2b81743f4e9d100aea6c791fa5e8de9933/pandas/core/generic.py#L3041
is too long. Could you please rewrite it as multi-line statement? It will fix one of the errors.
 Closed by https://github.com/pandas-dev/pandas/pull/57025