BUG: `DataFrame.explode` is failing on scalar `int` value.
- [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.

---

**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

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

```python
>>> import pandas as pd
>>> import numpy as np
>>> df = pd.DataFrame({0: [[0, 1, 2], 'foo', [], [3, 4]],
...                    1: 1,
...                    2: [['a', 'b', 'c'], np.nan, [], ['d', 'e']]})
>>> df
           0  1          2
0  [0, 1, 2]  1  [a, b, c]
1        foo  1        NaN
2         []  1         []
3     [3, 4]  1     [d, e]
>>> df.columns
Int64Index([0, 1, 2], dtype='int64')
>>> df.explode(0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/pgali/anaconda3/envs/cudf_dev/lib/python3.8/site-packages/pandas/core/frame.py", line 8229, in explode
    assert isinstance(column, (str, tuple))
AssertionError
>>> df.explode([0])
     0  1          2
0    0  1  [a, b, c]
0    1  1  [a, b, c]
0    2  1  [a, b, c]
1  foo  1        NaN
2  NaN  1         []
3    3  1     [d, e]
3    4  1     [d, e]
>>> 

```

#### Problem description

Looks like passing a scalar `int` to `column` is causing a failure in `DataFrame.explode`, but passing a list of int's is working.

#### Expected Output
```python
>>> df.explode(0)
     0  1          2
0    0  1  [a, b, c]
0    1  1  [a, b, c]
0    2  1  [a, b, c]
1  foo  1        NaN
2  NaN  1         []
3    3  1     [d, e]
3    4  1     [d, e]
```

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

<details>


INSTALLED VERSIONS
------------------
commit           : 5f648bf1706dd75a9ca0d29f26eadfbb595fe52b
python           : 3.8.10.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.11.0-27-generic
Version          : #29~20.04.1-Ubuntu SMP Wed Aug 11 15:58:17 UTC 2021
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.3.2
numpy            : 1.21.2
pytz             : 2021.1
dateutil         : 2.8.2
pip              : 21.2.4
setuptools       : 57.4.0
Cython           : 0.29.24
pytest           : 6.2.4
hypothesis       : 6.17.2
sphinx           : 4.1.2
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 3.0.1
IPython          : 7.27.0
pandas_datareader: None
bs4              : 4.9.3
bottleneck       : None
fsspec           : 2021.07.0
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 5.0.0
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : 0.53.1


</details>
