fix .net8 format with conditionals

SpotifyAPI.Web.Auth/AuthException.cs

@@ -1,7 +1,10 @@
+using System;
+using System.Runtime.Serialization;
+
 namespace SpotifyAPI.Web.Auth
 {
-  [System.Serializable]
-  public class AuthException : System.Exception
+  [Serializable]
+  public class AuthException : Exception
   {
     public AuthException(string? error, string? state)
     {
@@ -9,10 +12,12 @@ namespace SpotifyAPI.Web.Auth
       State = state;
     }
     public AuthException(string message) : base(message) { }
-    public AuthException(string message, System.Exception inner) : base(message, inner) { }
-    protected AuthException(
-        System.Runtime.Serialization.SerializationInfo info,
-        System.Runtime.Serialization.StreamingContext context) : base(info, context) { }
+    public AuthException(string message, Exception inner) : base(message, inner) { }
+
+#if NET8_0_OR_GREATER
+    [Obsolete("This API supports obsolete formatter-based serialization. It should not be called or extended by application code.")]
+#endif
+    protected AuthException(SerializationInfo info, StreamingContext context) : base(info, context) { }
 
     public string? Error { get; set; }
     public string? State { get; set; }

SpotifyAPI.Web/Clients/SimplePaginator.cs

@@ -1,6 +1,6 @@
 using System;
 using System.Collections.Generic;
-#if NET8_0_OR_GREATER
+#if !NETSTANDARD2_0
 using System.Runtime.CompilerServices;
 #endif
 using System.Threading;

SpotifyAPI.Web/Clients/SpotifyClient.cs

@@ -1,6 +1,6 @@
 using System;
 using System.Collections.Generic;
-#if NET8_0_OR_GREATER
+#if !NETSTANDARD2_0
 using System.Runtime.CompilerServices;
 #endif
 using System.Threading;

SpotifyAPI.Web/Util/StringAttribute.cs

@@ -1,5 +1,5 @@
 using System;
-#if NET8_0_OR_GREATER
+#if !NETSTANDARD2_0
 using System.Diagnostics.CodeAnalysis;
 #endif
 using System.Linq;