Fix compilation error within the unit test

src/EditorFeatures/CSharpTest/UsePatternMatching/CSharpAsAndNullCheckTests_FixAllTests.cs

-// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
 using System.Threading.Tasks;
 using Roslyn.Test.Utilities;
@@ -14,7 +14,7 @@ public async Task FixAllInDocument1()
             await TestInRegularAndScriptAsync(
 @"class C
 {
-    void M()
+    int M()
     {
         string a;
         {|FixAllInDocument:var|} x = o as string;
@@ -40,7 +40,7 @@ void M()
 }",
 @"class C
 {
-    void M()
+    int M()
     {
         if (o is string x)
         {