Font Awesome Brand Icons do not work

Describe the bug

Brand icons from font-awesome do not render correctly.

To Reproduce

from flask import Flask, render_template_string

import folium

app = Flask(__name__)


@app.route("/")
def fullscreen():
    """Simple example of a fullscreen map."""
    m = folium.Map(location=[41, -71], zoom_start=4)

    folium.Marker(location=[41, -72],
        icon=folium.Icon(prefix='fa', icon='fa-heart')).add_to(m)

    folium.Marker(location=[41, -75],
        icon=folium.Icon(prefix='fa', icon='fa-bluetooth')).add_to(m)

    return m.get_root().render()


if __name__ == "__main__":
    app.run(debug=True)

Expected behavior

All icons to render correctly

Environment (please complete the following information):

• Browser: Firefox 140.15.0esr and Chromium 152.0.7977.64
• Jupyter Notebook or html files? Flask
• Python version: sys.version_info(major=3, minor=13, micro=5, releaselevel='final', serial=0)
• folium version: 0.19.5+dfsg
• branca version: 0.8.1

Additional context

It seems that the appropriate web font is not loaded. If I go to Web Developer Tools -> Inspector -> Fonts -> All Fonts on Page only https://cdn.jsdelivr.net/npm/@fortawesome/fontawesome-free@6.2.0/webfonts/fa-solid-900.woff2 is loaded and I believe the glyph for bluetooth is in https://cdn.jsdelivr.net/npm/@fortawesome/fontawesome-free@6.2.0/webfonts/fa-brands-400.woff2 so it isn't rendered correctly.

Screenshots

folium is maintained by volunteers. Can you help making a fix for this issue? Probably not

Start by running the Flask reproduction from the issue and inspecting the generated HTML and loaded Font Awesome web fonts in Firefox or Chromium. Trace how folium.Icon handles the fa prefix and compare the solid heart icon with the brand bluetooth icon. Done means both markers render correctly, with a regression check covering brand icons.