[BUG] Daily calendar backup leads to cancelled/resent event invites for a Microsoft365 account

### ⚠️ 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

1. Sync a Microsoft365 calendar into the Android calendar provider (have tested this with the official Outlook app and Nine Mail)
2. Enable daily calendar backup
3. Create a calendar event in the Microsoft365 calendar and set attendees so the event is sent out to them
4. After daily backup, check sent mails on Microsoft365 account- events cancellations get sent to attendees and sometimes rescheduled afterwards. Sometimes cancellations are being sent with no rescheduling.

### Expected behaviour

Daily calendar backups should quietly take a backup and not interfere with the calendar in any way otherwise (leaast of all lead to event cancellations.)

### Actual behaviour

For a synced Microsoft365 calendar, the daily backup leads to cancellations being sent to recipients of calendar invites. I have not tested if this is true for events in the Nextcloud calendar as they don't get sent out on my instance.

### Android version

13

### Device brand and model

Google Pixel 6a

### Stock or custom OS?

Custom (explain in "additional information")

### Nextcloud android app version

3.25.0

### Nextcloud server version

26.0.3

### Using a reverse proxy?

Yes

### Android logs

_No response_

### Server error logs

_No response_

### Additional information

Phone is on GrapheneOS, but this issue has plagued me on my previous phone with various Android versions and ROMs. I have changed mail apps, accused the MS Teams app, called MS support multiple times...
This morning, I finally caught the brief backup notification while it was ongoing and sure enough- a test event I had created got resent at exactly the same time right after.
Very happy I found the culprit, but having client meetings automatically cancelled is actually horrible and has led to uncomfortable situations...