Quick Fix / Code Action widget: ArrowDown invokes selectNextCodeAction but selection never moves

## Does this issue occur when all extensions are disabled?
Not yet tested (see repro steps — the keybinding log below shows the correct built-in command firing, so an extension conflict looks unlikely, but I can retest with `--disable-extensions` if useful).

## Steps to Reproduce

1. Open any file with an available Code Action / Quick Fix (e.g. a Python file with a Pyright/Ruff diagnostic).
2. Place the cursor on the diagnostic and trigger Quick Fix (`Alt+Enter`, mapped to `editor.action.quickFix`).
3. With the Code Action widget open, press `ArrowDown` repeatedly to move the selection to another action.

**Expected:** the highlighted item in the Code Action list advances on each `ArrowDown` press.

**Actual:** the highlighted item never moves — the first action stays selected no matter how many times `ArrowDown` is pressed. Selecting a different action is only possible by clicking it with the mouse.

## Keybinding troubleshooting log

Using `Developer: Toggle Keyboard Shortcuts Troubleshooting`, each `ArrowDown` press while the widget is open correctly resolves and invokes the built-in command — so the keybinding itself is not the problem, the command appears to have no visible effect on the widget:

```
[KeybindingService]: | Converted keydown event - modifiers: [], code: ArrowDown, keyCode: 18 ('DownArrow')
[KeybindingService]: | Resolving [ArrowDown]
[KeybindingService]: \ From 24 keybinding entries, matched selectNextCodeAction, when: codeActionMenuVisible, source: built-in.
[KeybindingService]: + Invoking command selectNextCodeAction.
```

(repeats identically on every subsequent `ArrowDown` press — `selectNextCodeAction` is invoked each time, but the list selection never advances.)

This looks similar to a past regression reported in #160062 (also "command invoked, no visible effect" for the Code Action widget), which suggests a regression rather than a new bug class.

## Version

- VS Code: 1.137.0 (`645f29cc3176500b4b5762ba887cf2a7f0ffdf2c`)
- OS: Linux x64 (Arch Linux, kernel 7.2.3-arch1-3)