Fix test comments (#47622)

src/Compilers/CSharp/Test/Semantic/Semantics/GenericConstraintsTests.cs

@@ -1827,7 +1827,7 @@ public void UnmanagedConstraint_Compilation_ReferenceType()
             var c = CreateCompilation("public class Test<T> where T : class, unmanaged {}");
 
             c.VerifyDiagnostics(
-                // (1,39): error CS8869: The 'unmanaged' constraint cannot be combined with the 'class' constraint
+                // (1,39): error CS0449: The 'unmanaged' constraint cannot be combined with the 'class' constraint
                 // public class Test<T> where T : class, unmanaged {}
                 Diagnostic(ErrorCode.ERR_TypeConstraintsMustBeUniqueAndFirst, "unmanaged").WithLocation(1, 39));
 
@@ -1845,7 +1845,7 @@ public void UnmanagedConstraint_Compilation_ValueType()
             var c = CreateCompilation("public class Test<T> where T : struct, unmanaged {}");
 
             c.VerifyDiagnostics(
-                // (1,40): error CS8869: The 'unmanaged' constraint cannot be combined with the 'struct' constraint
+                // (1,40): error CS0449: The 'unmanaged' constraint cannot be combined with the 'struct' constraint
                 // public class Test<T> where T : struct, unmanaged {}
                 Diagnostic(ErrorCode.ERR_TypeConstraintsMustBeUniqueAndFirst, "unmanaged").WithLocation(1, 40));