fix(caldav): allow listing of room and resource principals

[st3iny]

• Resolves: #

Summary

Follow-up to nextcloud/calendar#5961

We need to allow listing rooms and resources for the overview in calendar.

How to test?

1. Disable debug mode in your config.php.
2. Try to list rooms and resources in the Calendar app. => Doesn't work
3. Apply this PR.
4. Try again. => Works

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)