Revert "missing usings"

This reverts commit 3f58758.

Author: SimonCropp

src/DiffEngineTray.Tests/AsyncTimerTests.cs

@@ -5,13 +5,14 @@ public async Task It_calls_error_callback()
     {
         var errorCallbackInvoked = new TaskCompletionSource<bool>();
 
-        await using var timer = new AsyncTimer(
+        var timer = new AsyncTimer(
             callback: _ => throw new("Simulated!"),
             interval: TimeSpan.Zero,
             errorCallback: _ =>
             {
                 errorCallbackInvoked.SetResult(true);
             });
+
         Assert.True(await errorCallbackInvoked.Task);
     }
 
@@ -22,7 +23,7 @@ public async Task It_continues_to_run_after_an_error()
 
         var fail = true;
         var exceptionThrown = false;
-        await using var timer = new AsyncTimer(
+        var timer = new AsyncTimer(
             callback: _ =>
             {
                 if (fail)
@@ -50,7 +51,7 @@ public async Task Stop_cancels_token_while_in_callback()
         var callbackCanceled = false;
         var callbackStarted = new TaskCompletionSource<bool>();
         var stopInitiated = new TaskCompletionSource<bool>();
-        await using var timer = new AsyncTimer(
+        var timer = new AsyncTimer(
             callback: async token =>
             {
                 callbackStarted.SetResult(true);
@@ -74,7 +75,7 @@ public async Task Stop_waits_for_callback_to_complete()
     {
         var callbackCompleted = new TaskCompletionSource<bool>();
         var callbackTaskStarted = new TaskCompletionSource<bool>();
-        await using var timer = new AsyncTimer(
+        var timer = new AsyncTimer(
             callback: _ =>
             {
                 callbackTaskStarted.SetResult(true);