Current app is not considered correctly in `get_jazzmin_settings`

[PavelPancocha]

During this change: https://github.com/farridav/django-jazzmin/commit/3ed99883bfbf6a846d45a6418d25483516ad2e71#diff-2d17ef548c972fba2f55b0a493ab0c923e2553b70287684f2e814342d845261fL131-L135

The current app was omitted. It now uses admin_site settings for the first site of all admin sites. Original discussion: https://github.com/farridav/django-jazzmin/pull/406#discussion_r863743524