Fix DatetimeIndex and other docstring for missing period at the end of summary

[datapythonista]

Same as #132 but for the next docstrings:

pandas.IndexSlice: Summary does not end with a period
pandas.MultiIndex.names: Summary does not end with a period
pandas.MultiIndex.is_lexsorted: Summary does not end with a period
pandas.MultiIndex.reorder_levels: Summary does not end with a period
pandas.DatetimeIndex.snap: Summary does not end with a period
pandas.DatetimeIndex.to_perioddelta: Summary does not end with a period
pandas.DatetimeIndex.to_pydatetime: Summary does not end with a period
pandas.DatetimeIndex.to_series: Summary does not end with a period
pandas.TimedeltaIndex: Summary does not end with a period
pandas.PeriodIndex.is_leap_year: Summary does not end with a period
pandas.api.extensions.ExtensionArray._concat_same_type: Summary does not end with a period
pandas.api.extensions.ExtensionArray.dropna: Summary does not end with a period

[martinagvilas]

I would like to work on this

[martinagvilas]

Closing this issue because it was merged in pandas #28031