[Bug] add_hline and add_vline do not work with datetime and annotation_text #3494

import datetime
import plotly.graph_objects as go
figure = go.Figure()

figure.update_layout(
    yaxis=dict(
        type="date",
        tickformat='%H:%M',
    )
)

figure.add_hline(
    annotation_text="Recommended Daily Intake",
    y=datetime.datetime.now(),
)

  File "..../.venv/lib/python3.9/site-packages/plotly/shapeannotation.py", line 7, in _mean
    return float(sum(x)) / len(x)
TypeError: unsupported operand type(s) for +: 'int' and 'datetime.datetime'

>>> print(x)
[datetime.datetime(2021, 12, 2, 14, 3, 29, 780450), datetime.datetime(2021, 12, 2, 14, 3, 29, 780450)]

>>> sum([datetime.datetime(2021, 12, 2, 14, 3, 29, 780450), datetime.datetime(2021, 12, 2, 14, 3, 29, 780450)])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'datetime.datetime'