fix namespace

Author: Nigusu-Allehu

build/Shared/AotCompatibilityAttributes.cs

@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 #if !NET9_0_OR_GREATER
-namespace System.Runtime.CompilerServices
+namespace System.Diagnostics.CodeAnalysis
 {
     [AttributeUsage(AttributeTargets.Property, Inherited = false)]
     internal sealed class FeatureSwitchDefinitionAttribute : Attribute

build/Shared/NuGetFeatureFlags.cs

@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Runtime.CompilerServices;
+using System.Diagnostics.CodeAnalysis;
 using NuGet.Common;
 
 namespace NuGet.Shared