BUG: Repeated key words on datetime indexing methods (_parsed_string_to_bounds())
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [x] (optional) I have confirmed this bug exists on the master branch of pandas.

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Readed! I will know for next time 

#### Code Sample, a copy-pastable example

```python

There is no need for code, as the error is on the function having repeated keywords.
```

#### Problem description

There are two repeated keywords on the master/pandas/core/indexes/datetimes.py#L560 and #L561. 
I closed the issue #38121, as it is working fine, but as said, there are repeated keywords.

        valid_resos = {
            "year",
            "month",
            "quarter",
            "day",
            "hour",
            "minute",
            "second",
            "minute",
            "second",
            "millisecond",
            "microsecond",
        }

it should be:

        valid_resos = {
            "year",
            "month",
            "quarter",
            "day",
            "hour",
            "minute",
            "second",
            "millisecond",
            "microsecond",
        }

Reference here:

https://github.com/pandas-dev/pandas/blob/0b16fb308b7808f193a5a8d86d71b6e57d99d4e7/pandas/core/indexes/datetimes.py#L560-L561

#### Expected Output

        valid_resos = {
            "year",
            "month",
            "quarter",
            "day",
            "hour",
            "minute",
            "second",
            "millisecond",
            "microsecond",
        }

#### Output of ``pd.show_versions()``

 There is no need for versions. Pandas code in this case is fine. Just two repeated lines.

