Gallery examples fail with pandas >=2.1 due to invalid frequency 'ME'

[aman-coder03]

When building the documentation with pandas 2.1.4, 2 gallery examples in the irradiance-transposition section fail during execution plot_transposition_gain.py and plot_seasonal_tilt.py

Both examples use:
.resample("ME") which raises ValueError: Invalid frequency: ME

Example

import pandas as pd
import numpy as np

idx = pd.date_range("2020-01-01", periods=100, freq="H")
s = pd.Series(np.random.rand(100), index=idx)
s.resample("ME").sum()

on pandas 2.1.4 this results in ValueError: Invalid frequency: ME

It appears that "ME" is no longer recognized as a valid frequency alias in recent pandas versions
Happy to open a PR, if this change is appropriate.