Flaky test check_runtimes: [04:45:46]RUNTIME: Cannot read null.assigned_equipment_preset - code/game/objects/items/devices/radio/headset.dm@372

Flaky tests were detected in [this test run](https://github.com/cmss13-devs/cmss13/actions/runs/23832306533/attempts/1). This means that there was a failure that was cleared when the tests were simply restarted.
Failures:
```
check_runtimes: [04:45:46]RUNTIME: Cannot read null.assigned_equipment_preset - code/game/objects/items/devices/radio/headset.dm@372 at code/defines/../modules/unit_tests/check_runtimes.dm:10
```

Start with the failing test run and read code/defines/../modules/unit_tests/check_runtimes.dm:10 alongside code/game/objects/items/devices/radio/headset.dm:372. Reproduce the check_runtimes failure and investigate the null assigned_equipment_preset access. Done means the test no longer reports this runtime failure across repeated runs.

Written by the indexing model from the issue text.