Backup of Calendar-not working.

### ⚠️ Before posting ⚠️

- [x] This is a **bug**, not a question or an enhancement.
- [x] I've [searched for similar issues](https://github.com/nextcloud/android/issues) and didn't find a duplicate.
- [x] I've written a clear and descriptive title for this issue, not just "Bug" or "Crash".
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/).

### Steps to reproduce

settings
- contacts and calendar backup
- all in position "ON"
- backup now (also as automatic daily)
- wait
- contacts are backed up
- calendar are not

### Expected behaviour

backup of calendar completed

### Actual behaviour

backup of calendar occurs not

### Android version

13

### Device brand and model

realme / redmi

### Stock or custom OS?

Stock

### Nextcloud android app version

20251223

### Nextcloud server version

32.0.3

### Using a reverse proxy?

No

### Android logs

_No response_

### Server error logs

```bash

```

### Additional information

that is more than single version ... last occurred in September (what version was installed at moment - hard to tell)

- build in use "devel" from f-droid
- all permissions on device granted