Fix default Roboto font not being found by the matplotlib FontManager

[madmiraal]

Fixes #115

requirements.txt:

sphinx==7.2.6
sphinxext-opengraph==0.9.0
matplotlib==3.8.2

With a default conf.py created using sphinx-quickstart (minus the comments) and adding the sphinxext-opengraph extension:

project = 'Test'
copyright = '2023, Test Authors'
author = 'Test Authors'

extensions = [
    "sphinxext.opengraph",
]

templates_path = ['_templates']
exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store']

html_theme = 'alabaster'
html_static_path = ['_static']

Running make html now creates a beautiful Social Card: