git help config says (emphasis mine):

Includes
The include and includeIf sections allow you to include config directives from another source. These sections behave identically to each other with the exception that includeIf sections may be ignored if their condition does not evaluate to true; see "Conditional includes"
below.

 You can include a config file from another by setting the special include.path (or includeIf.*.path) variable to the name of the file to be included. The variable takes a pathname as its value, and is subject to tilde expansion. **These variables can be given multiple times.**

Which means this is a valid config:

[include]
  path = ~/.config/git/maintenance.config
  path = ~/.config/git/my-config

But this isn't handled by GitPython today, only one path entry is returned.