Fix build

Author: davidwengier

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Formatting_NetFx/TestHtmlFormatter.cs

@@ -6,21 +6,20 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor.ProjectSystem;
-using Microsoft.AspNetCore.Razor.Threading;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
 
 namespace Microsoft.AspNetCore.Razor.LanguageServer.Formatting;
 
 internal class TestHtmlFormatter : IHtmlFormatter
 {
-    public Task<ImmutableArray<TextChange>> GetDocumentFormattingEditsAsync(IDocumentSnapshot documentSnapshot, Uri uri, FormattingOptions options, CancellationToken cancellationToken)
+    public Task<ImmutableArray<TextChange>?> GetDocumentFormattingEditsAsync(IDocumentSnapshot documentSnapshot, Uri uri, FormattingOptions options, CancellationToken cancellationToken)
     {
-        return SpecializedTasks.EmptyImmutableArray<TextChange>();
+        return Task.FromResult<ImmutableArray<TextChange>?>([]);
     }
 
-    public Task<ImmutableArray<TextChange>> GetOnTypeFormattingEditsAsync(IDocumentSnapshot documentSnapshot, Uri uri, Position position, string triggerCharacter, FormattingOptions options, CancellationToken cancellationToken)
+    public Task<ImmutableArray<TextChange>?> GetOnTypeFormattingEditsAsync(IDocumentSnapshot documentSnapshot, Uri uri, Position position, string triggerCharacter, FormattingOptions options, CancellationToken cancellationToken)
     {
-        return SpecializedTasks.EmptyImmutableArray<TextChange>();
+        return Task.FromResult<ImmutableArray<TextChange>?>([]);
     }
 }