BUG: Date objects cannot be compared against a DatetimeIndex
- [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.

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

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

Version 1.0.5
```python
holidays = USFederalHolidayCalendar().holidays()
>>> datetime.datetime(2018, 7, 4) in holidays
True
>>> datetime.date(2018, 7, 4) in holidays
True
>>> pd.__version__
'1.0.5'
```

Version 1.1.0
```python
holidays = USFederalHolidayCalendar().holidays()
>>> datetime.datetime(2018, 7, 4) in holidays
True
>>> datetime.date(2018, 7, 4) in holidays
False
>>> pd.__version__
'1.1.0'
>>>
```

#### Problem description

On version 1.0.5 it was possible to compare via __contains__ a *datetime.date* object against a DatetimeIndex, this behavior is not true anymore for the 1.1.0, is this an expected behavior to allow only recognized scalars objects?

#### Expected Output

Allow dates to be compared with 00:00:00 time.

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

<details>

INSTALLED VERSIONS
------------------
commit           : d9fff2792bf16178d4e450fe7384244e50635733
python           : 3.6
OS               : Darwin

pandas           : 1.1.0
numpy            : 1.19.1
Cython           : None
</details>
