Address code review feedback

Co-authored-by: rolfbjarne <249268+rolfbjarne@users.noreply.github.com>

Author: Copilot

msbuild/Xamarin.MacDev.Tasks/Tasks/ComputeInstructionSet.cs

@@ -235,6 +235,8 @@ public override bool Execute ()
 
 				var instructionSet = ComputeMinimumInstructionSet (Platform, SupportedOSPlatformVersion);
 				if (!string.IsNullOrEmpty (instructionSet)) {
+					// The null-forgiving operator is required here because the compiler doesn't understand
+					// that !string.IsNullOrEmpty guarantees non-null
 					InstructionSet = instructionSet!;
 					Log.LogMessage (MessageImportance.Low, $"Computed instruction set '{InstructionSet}' for {PlatformName} {SupportedOSPlatformVersion}");
 				} else {

tests/msbuild/Xamarin.MacDev.Tasks.Tests/TaskTests/ComputeInstructionSetTaskTests.cs

@@ -93,8 +93,6 @@ public void TestVeryOldOSVersion ()
 			var task = CreateTask (ApplePlatform.iOS);
 			task.SupportedOSPlatformVersion = "9.0";
 
-			ExecuteTask (task);
-
 			// iOS 9 was supported by iPhone 4s (A5), but we don't have data for that era
 			// The task should handle this gracefully
 			ExecuteTask (task);