chore: Update color of invertocat icon

Author: jo-mueller

icons/invertocat.svg

@@ -175,8 +175,10 @@ def render_authors_md():
 
     markdown_authors = """"""
 
+    # The invertocat icon was downloaded from https://brand.github.com/foundations/logo
+    # and colored in grey according to the guidelines under the "Color" section.
     orcid_icon = "https://orcid.org/assets/vectors/orcid.logo.icon.svg"
-    github_icon = "https://github.githubassets.com/favicons/favicon.svg"
+    github_icon = "icons/invertocat.svg"
 
     for idx, author in enumerate(authors):
         name = author['name']