fix: remove caching in fetchListOfGroups

[kesselb]

• Resolves: #42195

Summary

When using nested groups without a memberof overlay, then fetchListOfGroups is called from getGroupsByMember without applying the group filter.

In some setups, the "unfiltered" result is then written back to the group mapping table. That might cause random "An administrator removed you from group" activities.

I was unable to replicate it locally, but we got the feedback that the random activities stopped with the patch applied.

Ref: https://github.com/nextcloud/server/issues/42195

TODO

• [ ] CI & Tests
• [ ] Review

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• [ ] Tests (unit, integration, api and/or acceptance) are included
• [ ] Screenshots before/after for front-end changes
• [ ] Documentation (manuals or wiki) has been updated or is not required
• [ ] Backports requested where applicable (ex: critical bugfixes)