Pack style engine width not correct size on linux?

### Describe the bug

On linux, when I set the width of labels using the Pack style engine, the width isn't correct. Here is a screenshot:

### Steps to reproduce

1. Create a toga label and use the pack style engine to set the width to 2 (I only tested it with a width of 2)
2. Run the toga app on linux

### Expected behavior

The expected behavior is the toga label should be cut off because the width is too short for the text, but its not

### Screenshots

_No response_

### Environment

- Operating System: Ubuntu 25.04
- Python version: 3.13.3
- Software versions:
- Briefcase: 0.3.25
- Toga: 0.5.2

### Logs

_No response_

### Additional context

_No response_

Reproduce the issue on Ubuntu with a Toga label using the pack style engine and width 2, then trace the label sizing path. Compare the rendered width with the expected clipped text behavior; done means the label is cut off when its configured width is too small.

Written by the indexing model from the issue text.