In practice this should also work. Do keep in mind if you just add this to your init.el then this will not persist if you re-create the scratch buffer.

If we are already experimenting with different ideas, this should also work (and gives a hint of how you want to fix the issue upstream):

    (define-advice get-scratch-buffer-create (:filter-return (buf) trusted)
      (with-current-buffer buf
        (setq-local trusted-content :all))
      buf)