15.6 の場合は、 root で下記のコマンドを実行してください:
zypper addrepo https://download.opensuse.org/repositories/home:crameleon:branches:devel:languages:python:backports/15.6/home:crameleon:branches:devel:languages:python:backports.repo
zypper refresh
zypper install python-django-storages
15.5 の場合は、 root で下記のコマンドを実行してください:
zypper addrepo https://download.opensuse.org/repositories/home:crameleon:branches:devel:languages:python:backports/15.5/home:crameleon:branches:devel:languages:python:backports.repo
zypper refresh
zypper install python-django-storages