Bump cdav-library from `4e6bc30` to `c087ab5`

Bumps [cdav-library](https://github.com/nextcloud/cdav-library) from `4e6bc30` to `c087ab5`.
- [Release notes](https://github.com/nextcloud/cdav-library/releases)
- [Commits](https://github.com/nextcloud/cdav-library/compare/4e6bc30723718a5dd8a1de2487577b286ccf2821...c087ab5af44d1b09c6a92a1054585a9a67796f9e

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