Stop awaiting decompiles those tests never read

The four `WaitForDecompiledTextAsync` calls in PreviewTabPromotionTests
asserted only on dock structure -- SourceNode, IsPreview, tab count,
Content reference -- never on decompiled Text. Those values are set
synchronously by ShowSelectedNode before DecompileAsync's first await
returns, so the ~25s wait was pure dead weight. Worse, the fire-and-forget
DecompileAsync kept chewing CPU after the test returned and contended on
the ThreadPool with the next test's decompile, which is what pushed the
same workload from 12-16s in isolation to 24-28s in full-suite -- right
up against the 30s budget. One slow GC pause and PinCurrentTab_Flips
timed out at 30.997s exactly.

ILSpy.Tests/Docking/PreviewTabPromotionTests.cs

@@ -94,7 +94,7 @@ public class PreviewTabPromotionTests
 		var typeNode = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
 		vm.AssemblyTreeModel.SelectNode(typeNode);
-		await vm.DockWorkspace.WaitForDecompiledTextAsync(System.TimeSpan.FromSeconds(60));
+		vm.DockWorkspace.SettleSelection();
 		ReferenceEquals(previousMainTab.SourceNode, typeNode).Should().BeTrue(
 			"baseline: tree selection populated MainTab with the chosen node");
 
@@ -135,7 +135,7 @@ public class PreviewTabPromotionTests
 		var typeA = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Linq", "System.Linq", "System.Linq.Enumerable");
 		vm.AssemblyTreeModel.SelectNode(typeA);
-		await vm.DockWorkspace.WaitForDecompiledTextAsync(System.TimeSpan.FromSeconds(60));
+		vm.DockWorkspace.SettleSelection();
 		var pinnedTab = factory.MainTab!;
 		var pinnedContent = pinnedTab.Content;
 
@@ -150,7 +150,7 @@ public class PreviewTabPromotionTests
 		var typeB = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Private.Uri", "System", "System.Uri");
 		vm.AssemblyTreeModel.SelectNode(typeB);
-		await vm.DockWorkspace.WaitForDecompiledTextAsync(System.TimeSpan.FromSeconds(60));
+		vm.DockWorkspace.SettleSelection();
 
 		// New tab spawned beside the pinned one.
 		vm.DockWorkspace.Documents!.VisibleDockables!.Count.Should().Be(tabCountBeforeSelection + 1,
@@ -595,7 +595,7 @@ public class PreviewTabPromotionTests
 		var typeB = vm.AssemblyTreeModel.FindNode<TypeTreeNode>(
 			"System.Private.Uri", "System", "System.Uri");
 		vm.AssemblyTreeModel.SelectNode(typeB);
-		await vm.DockWorkspace.WaitForDecompiledTextAsync(System.TimeSpan.FromSeconds(60));
+		vm.DockWorkspace.SettleSelection();
 
 		vm.DockWorkspace.Documents!.VisibleDockables!.Count.Should().Be(tabCountBefore + 1,
 			"selecting a tree node while a frozen tab is active must spawn a new preview tab");

ILSpy/Docking/DockWorkspace.cs

@@ -1076,6 +1076,17 @@ namespace ILSpy.Docking
 		/// a fresh preview tab inside <see cref="ShowSelectedNode"/>. Re-clicking the same
 		/// node after pin is a no-op (the dedupe activates the pinned tab).
 		/// </summary>
+		/// <summary>
+		/// Pump dispatcher jobs so synchronously-set selection state (SourceNode, IsPreview,
+		/// tab count, Content reference) finishes propagating, without awaiting the
+		/// fire-and-forget DecompileAsync. Tests that assert on dock structure can use this
+		/// instead of WaitForDecompiledTextAsync to avoid the multi-second decompile wait.
+		/// </summary>
+		public void SettleSelection()
+		{
+			Avalonia.Threading.Dispatcher.UIThread.RunJobs();
+		}
+
 		public void PinCurrentTab()
 		{
 			if (factory.PinCurrentMainTab() is null)