> +       (modify-phases %standard-phases
> +         (add-before 'check 'fix-library-loading
> +           (lambda _
> +             (setenv "PYTHONPATH" (string-append (getenv "PYTHONPATH") ":."))
> +             #t))

Returning #t is not required anymore, please remove.  The warning that results if
a phase doesn't return #t has been removed on core-updates.

No other comments, thanks for updating.
Warning: I haven't tested the patch.

Greetings,
Maxime.