Add the changed files between two commits to the response of the compare API, part of forgejo/forgejo#6460
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6461
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Angel Nunez Mencias <git@angelnu.com>
Co-committed-by: Angel Nunez Mencias <git@angelnu.com>