REGR: fillna on datetime64[ns, UTC] column hits RecursionError
#### Code Sample

```python
from datetime import datetime, timezone
import pandas as pd

df = pd.DataFrame(range(31))
df["dt"] = pd.date_range("2020/12/01", "2020/12/31", tz="UTC")
df["dt"].iloc[5] = pd.NaT
df["dt"] = df["dt"].fillna(datetime(1980, 1, 1, tzinfo=timezone.utc))
```

#### Problem description

pandas 1.2.0 is throwing a RecursionError while attempting to `fillna` on a `datetime64[ns, UTC]` column.  Same code worked in prior releases.

```
raceback (most recent call last):
  File "recursion.py", line 7, in <module>
    df["dt"] = df["dt"].fillna(utc(1980, 1, 1, tzinfo=timezone.utc))
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/series.py", line 4433, in fillna
    return super().fillna(
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/generic.py", line 6403, in fillna
    new_data = self._mgr.fillna(
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/managers.py", line 621, in fillna
    return self.apply(
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/managers.py", line 427, in apply
    applied = getattr(b, f)(**kwargs)
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/blocks.py", line 461, in fillna
    return self.split_and_operate(None, f, inplace)
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/blocks.py", line 516, in split_and_operate
    nv = f(mask, new_values, None)
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/blocks.py", line 459, in f
    return block.fillna(value, limit=limit, inplace=inplace, downcast=None)
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/blocks.py", line 461, in fillna
    return self.split_and_operate(None, f, inplace)
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/blocks.py", line 516, in split_and_operate
    nv = f(mask, new_values, None)
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/blocks.py", line 459, in f
    return block.fillna(value, limit=limit, inplace=inplace, downcast=None)
...snipped...
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/blocks.py", line 441, in fillna
    if self._can_hold_element(value):
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/internals/blocks.py", line 2267, in _can_hold_element
    tipo = maybe_infer_dtype_type(element)
  File "/opt/miniconda3/envs/prod/lib/python3.8/site-packages/pandas/core/dtypes/cast.py", line 924, in maybe_infer_dtype_type
    elif is_list_like(element):
  File "pandas/_libs/lib.pyx", line 1033, in pandas._libs.lib.is_list_like
  File "pandas/_libs/lib.pyx", line 1038, in pandas._libs.lib.c_is_list_like
  File "/opt/miniconda3/envs/prod/lib/python3.8/abc.py", line 98, in __instancecheck__
    return _abc_instancecheck(cls, instance)
RecursionError: maximum recursion depth exceeded in comparison

```

#### Expected Output

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

<details>

pd.show_versions()
/opt/miniconda3/envs/prod/lib/python3.8/site-packages/_distutils_hack/__init__.py:30: UserWarning: Setuptools is replacing distutils.
  warnings.warn("Setuptools is replacing distutils.")

INSTALLED VERSIONS
------------------
commit           : 3e89b4c4b1580aa890023fc550774e63d499da25
python           : 3.8.6.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.18.0-240.8.1.el8_3.x86_64
Version          : #1 SMP Fri Dec 4 12:24:03 EST 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.2.0
numpy            : 1.19.4
pytz             : 2020.5
dateutil         : 2.8.1
pip              : 20.3.3
setuptools       : 50.0.0.post20200830
Cython           : 0.29.21
pytest           : 6.2.1
hypothesis       : None
sphinx           : 3.4.1
blosc            : None
feather          : None
xlsxwriter       : 1.3.7
lxml.etree       : 4.6.2
html5lib         : 1.1
pymysql          : None
psycopg2         : 2.8.6 (dt dec pq3 ext lo64)
jinja2           : 2.11.2
IPython          : 7.19.0
pandas_datareader: None
bs4              : 4.9.3
bottleneck       : None
fsspec           : 0.8.5
fastparquet      : None
gcsfs            : None
matplotlib       : 3.3.3
numexpr          : None
odfpy            : None
openpyxl         : 3.0.5
pandas_gbq       : None
pyarrow          : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.3
sqlalchemy       : 1.3.22
tables           : None
tabulate         : None
xarray           : 0.16.2
xlrd             : 1.2.0
xlwt             : 1.3.0
numba            : 0.52.0

</details>

Thank you.