[Awake] Fix issue with timed mode not expiring correctly (#43785)

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## Summary of the Pull Request
Resolves an issue with the timed mode's expiry not completing correctly.

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## PR Checklist

- [x] Closes: #43775
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## Detailed Description of the Pull Request / Additional comments
This was because of my recent change to the timed mode. The `Subscribe`
method on the `Observable` interval accidentally wired the completion
logic to the **Error** handler instead of the **Completion** handler
because of the use of a discard `_` instead of an empty parameter list
`()`. As a result of the incorrect overload being called, Awake stayed
in the Timed state despite the timer reaching zero.

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## Validation Steps Performed
Confirmed that the timed mode times out and exits upon expiry.

src/modules/awake/Awake/Core/Manager.cs

@@ -350,7 +350,7 @@ namespace Awake.Core
                             TrayHelper.TimedIcon,
                             TrayIconAction.Update);
                     },
-                    _ => HandleTimerCompletion("timed"),
+                    () => HandleTimerCompletion("timed"),
                     _tokenSource.Token);
         }