Piefed unable to edit image post urls

### Bug Description

On piefed, create a post with an external image url. Then edit it and try to change the url. Edit seems to be successful but is not saved. Editing the same post via the Web UI works. 

### Expected Behaviour

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### Steps to Reproduce

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### Additional Context

_No response_

### App Version

_No response_

### Device

Pixel 9a 

### OS

Grapheneos 