Adding limit to matplotlib.

Author: ndilalla

.github/workflows/docs.yml

@@ -34,7 +34,7 @@ jobs:
 
           python -m pip install --upgrade pip wheel
 
-          python -m pip install numpy numba tempita jupytext jupyterthemes jupyter_latex_envs papermill matplotlib astropy pandas tables healpy
+          python -m pip install numpy numba tempita jupytext jupyterthemes jupyter_latex_envs papermill "matplotlib<3.9" astropy pandas tables healpy
           python -m pip install ebltable black cython pkgconfig h5py