fix: disallow calendar name change by non-owner

[DeepDiver1975]

Description

On a shared calendar it was possible to change the calendar name by a user who had only read access.

How Has This Been Tested?

• share calendar read only with an other user
• send displayname change PROPPATCH to the original calendar url but with the credentials of the sharee

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Database schema changes (next release will require increase of minor version instead of patch)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:
• Changelog item, see TEMPLATE

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.