Bump cdav-library from `f8d2318` to `b81b410`

Bumps [cdav-library](https://github.com/nextcloud/cdav-library) from `f8d2318` to `b81b410`.
- [Release notes](https://github.com/nextcloud/cdav-library/releases)
- [Commits](https://github.com/nextcloud/cdav-library/compare/f8d2318e4c7bcda196e8bb8fc508c46747744f05...b81b4107c6af8df619cb8e726401680b60ef0098

)

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