Transient window always resets the setting to true

Testing #335726

I'm guessing this issue is by design.
After running through the steps below, the New Worktree checkbox is still checked. I believe it's because transient always uses a different temp directory on Windows. Toggling the user-level `sessions.useWorktree` setting to `false` and reloading the Agents window finally unchecked the box.

```text
Close the Agents Window
Open the terminal and run code-insiders --agents --transient
...
Confirm that the "New Worktree" checkbox is not set
```