Local test failure plotting.test_datetimelike.test_ts_plot_with_tz
After running:
```
(venv-pandas) $ pytest pandas/tests/plotting/test_datetimelike.py -k "test_ts_plot_with_tz"
```

I got a test failure.

Test log:

<details> 

```
================================================== FAILURES ==================================================
___________________________________ TestTSPlot.test_ts_plot_with_tz['UTC'] ___________________________________

self = <pandas.tests.plotting.test_datetimelike.TestTSPlot object at 0x63f623915bb0>, tz_aware_fixture = 'UTC'

    @pytest.mark.slow
    def test_ts_plot_with_tz(self, tz_aware_fixture):
        # GH2877, GH17173, GH31205, GH31580
        tz = tz_aware_fixture
        index = date_range("1/1/2011", periods=2, freq="H", tz=tz)
        ts = Series([188.5, 328.25], index=index)
        with tm.assert_produces_warning(None):
            _check_plot_works(ts.plot)
            ax = ts.plot()
            xdata = list(ax.get_lines())[0].get_xdata()
            # Check first and last points' labels are correct
>           assert (xdata[0].hour, xdata[0].minute) == (0, 0)
E           AttributeError: 'numpy.datetime64' object has no attribute 'hour'

pandas/tests/plotting/test_datetimelike.py:57: AttributeError
```

</details>

---

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

<details>

INSTALLED VERSIONS
------------------
commit           : 4e5e73e2318a1221eb56ae7e68688278ca87ca6f
python           : 3.8.1.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.4.19.a-1-hardened
machine          : x86_64
processor        : 
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.1.0.dev0+635.g4e5e73e23
numpy            : 1.18.1
pytz             : 2019.3
dateutil         : 2.8.1
pip              : 20.0.2
setuptools       : 45.2.0
Cython           : 0.29.15
pytest           : 5.3.5
hypothesis       : 5.5.4
sphinx           : 2.4.3
blosc            : 1.8.3
feather          : None
xlsxwriter       : 1.2.8
lxml.etree       : 4.5.0
html5lib         : 1.0.1
pymysql          : None
psycopg2         : None
jinja2           : 2.11.1
IPython          : 7.12.0
pandas_datareader: None
bs4              : 4.8.2
bottleneck       : 1.3.2
fastparquet      : 0.3.3
gcsfs            : None
lxml.etree       : 4.5.0
matplotlib       : 3.1.3
numexpr          : 2.7.1
odfpy            : None
openpyxl         : 3.0.1
pandas_gbq       : None
pyarrow          : 0.16.0
pytables         : None
pytest           : 5.3.5
pyxlsb           : None
s3fs             : 0.4.0
scipy            : 1.4.1
sqlalchemy       : 1.3.13
tables           : 3.6.1
tabulate         : 0.8.6
xarray           : 0.15.0
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.2.8
numba            : 0.48.0


</details>

