Placeholders are not changed

### Describe the issue

Having a .po base file, downloading in a different format will not change the placeholder syntax

### I already tried

- [X] I've read and searched [the documentation](https://docs.weblate.org/).
- [X] I've searched for similar filed issues in this repository.

### Steps to reproduce the behavior

Having a .po base file, downloading in a different format will not change the placeholder syntax

### Expected behavior

_No response_

### Screenshots

_No response_

### Exception traceback

_No response_

### How do you run Weblate?

Docker container

### Weblate versions

_No response_

### Weblate deploy checks

_No response_

### Additional context

_No response_