Assert the search pane's DataContext before checking the progress binding

ProgressBar.IsIndeterminate defaults to false, so the "nothing is running
yet" assertion would also pass against a pane whose DataContext is not
the resolved SearchPaneModel, and the failure would only surface one
line later, blamed on the binding direction rather than on the missing
DataContext.

Assisted-by: Claude:claude-fable-5:Claude Code

ILSpy.Tests/Search/SearchProgressTests.cs

@@ -121,6 +121,7 @@ public class SearchProgressTests
 		// is an infinite animation, and one that ran while idle would keep the render clock
 		// busy for as long as the pane exists.
 		var search = AppComposition.Current.GetExport<SearchPaneModel>();
+		pane.DataContext.Should().BeSameAs(search, "the indicator binds to the pane's own model; anything else makes the assertions below meaningless");
 		progress!.IsIndeterminate.Should().BeFalse("nothing is running yet");
 		search.IsSearching = true;
 		Dispatcher.UIThread.RunJobs();