BUG: Datetime MultiIndex Regression
- [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.

---

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

```python
import pandas

date = pandas.Timestamp("2000")
x = pandas.DataFrame([
    ["a", date, 1],
], columns=["a", "b", "c"]).set_index(["a", "b"])["c"]
x.loc[:, [date]]


InvalidIndexError: [Timestamp('2000-01-01 00:00:00')]
```

#### Problem description

The problem stems from `pandas.DatetimeIndex.get_loc` raising a `InvalidIndexError` in `1.*` instead of a `TypeError` as in `0.25.3`

#### 0.25.3

```python                                                                                                                                                                                        
import pandas
level_index = pandas.DatetimeIndex(['2000-01-01'], dtype='datetime64[ns]', name='b', freq=None)
key = [pandas.Timestamp('2000-01-01 00:00:00')]
level_index.get_loc(key)

...
TypeError: Cannot convert input [[Timestamp('2000-01-01 00:00:00')]] of type <class 'list'> to Timestamp
```

#### 1.1.0

```python                                                                                                                                                                                        
import pandas
level_index = pandas.DatetimeIndex(['2000-01-01'], dtype='datetime64[ns]', name='b', freq=None)
key = [pandas.Timestamp('2000-01-01 00:00:00')]
level_index.get_loc(key)

...
InvalidIndexError: [Timestamp('2000-01-01 00:00:00')]
```

Previously the `TypeError` was handled by https://github.com/pandas-dev/pandas/blob/23b1717a14f185e3512607d33cdba17bfddfd064/pandas/core/indexing.py#L1078

#### Expected Output

I would expect this to behave similar to `0.25.3` which is valid indexing synatx.

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

<details>

INSTALLED VERSIONS
------------------
commit           : d9fff2792bf16178d4e450fe7384244e50635733
python           : 3.6.11.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.4.0-42-generic
Version          : #46~18.04.1-Ubuntu SMP Fri Jul 10 07:21:24 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : C.UTF-8
LANG             : C.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.1.0
numpy            : 1.16.2
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.2.2
setuptools       : 49.6.0.post20200814
Cython           : 0.29.21
pytest           : 5.3.5
hypothesis       : None
sphinx           : 3.2.1
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : 4.5.2
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.16.1
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.3.1
numexpr          : 2.7.1
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 0.12.0-RAY
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.1
sqlalchemy       : 1.3.19
tables           : 3.5.1
tabulate         : None
xarray           : 0.15.0
xlrd             : None
xlwt             : None
numba            : None



</details>
