Suppress cancellation warnings in tests

Add targeted `ReSharper disable once MethodSupportsCancellation` suppressions in test cases that intentionally omit cancellation tokens. The surrounding comments explain that passing tokens here can cancel scheduling or short-circuit shutdown waits, causing flaky `TaskCanceledException` behavior on CI.

Author: SimonCropp

src/DiffEngine.Tests/InlineApplierTests.cs

@@ -214,6 +214,7 @@ public async Task ContentIsNeverObservedHalfWritten()
             // `await reader` throwing TaskCanceledException - which is what made this fail on CI,
             // on all three OSes, while passing on any machine with a spare core. The loop already
             // exits on the token, which is the only cancellation this ever wanted
+            // ReSharper disable once MethodSupportsCancellation
             var reader = Task.Run(
                 () =>
                 {

src/DiffEngine.Tests/PendingFilesFallbackTests.cs

@@ -55,6 +55,10 @@ public async Task ADeadPiperFallsThroughToTheQueueOwner()
             await cancel.CancelAsync();
             try
             {
+                // No token: the line above already cancelled it, so passing it here would
+                // return before the listener had unwound rather than waiting for it to. The
+                // timeout is what bounds the drain
+                // ReSharper disable once MethodSupportsCancellation
                 await listening.WaitAsync(TimeSpan.FromSeconds(5));
             }
             catch (Exception exception)

src/DiffEngine.Tests/ViewerProtocolTests.cs

@@ -683,6 +683,7 @@ public async Task ASlowExchangeDoesNotBlockTheNext()
             // No token on Task.Run: it cancels the scheduling rather than the delegate, so a pool
             // that had not picked this up before the cancel in the finally would leave the task
             // Canceled and the await below throwing. TrySend is blocking and takes no token anyway
+            // ReSharper disable once MethodSupportsCancellation
             var accepting = Task.Run(() =>
                 ViewerClient.TrySend(new(ViewerVerb.Accept, "key"), out var slow, server.Port, hold)
                     ? slow

src/DiffEngineTray.Tests/SettingsWriteTests.cs

@@ -23,6 +23,11 @@ public async Task The_file_is_never_observed_missing()
         var missing = 0;
         var looks = 0;
         var unreadable = new ConcurrentBag<string>();
+        // No token on Task.Run. It cancels the scheduling rather than the delegate, so a pool
+        // that had not yet picked this up when the cancel lands leaves the task Canceled and
+        // `await reader` throwing. The loop already exits on the token, which is the only
+        // cancellation this ever wanted
+        // ReSharper disable once MethodSupportsCancellation
         var reader = Task.Run(
             () =>
             {