[red-knot] Default playground to Python 3.13 for real (#16956)
## Summary
Default to 3.13 for good.
I incorrectly used `workspace.updateOptions` instead of `updateOptions`
where the latter has a fallback.
## Test Plan
```py
import os
import sys
reveal_type(sys.version_info.minor)
```
reveals 13 on initial page load
