Bump cdav-library from `84d7146` to `a20daad`

Bumps [cdav-library](https://github.com/nextcloud/cdav-library) from `84d7146` to `a20daad`.
- [Release notes](https://github.com/nextcloud/cdav-library/releases)
- [Commits](https://github.com/nextcloud/cdav-library/compare/84d71460310056c1d61d07f02f2d4d14da8860fe...a20daadaec9eb4ddc2e874bac345cc1b1d28fa04

)

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