Fix conflicts

src/libraries/System.Runtime.Extensions/ref/System.Runtime.Extensions.Forwards.cs

@@ -77,4 +77,4 @@
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Security.Permissions.SecurityAction))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Security.Permissions.SecurityAttribute))]
 [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Security.Permissions.SecurityPermissionAttribute))]
-// [assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Security.Permissions.SecurityPermissionFlag))]
+[assembly:System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Security.Permissions.SecurityPermissionFlag))]

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -6609,8 +6609,8 @@ public BufferedStream(System.IO.Stream stream, int bufferSize) { }
         public override long Length { get { throw null; } }
         public override long Position { get { throw null; } set { } }
         public System.IO.Stream UnderlyingStream { get { throw null; } }
-        public override System.IAsyncResult BeginRead(byte[] buffer, int offset, int count, System.AsyncCallback callback, object? state) { throw null; }
-        public override System.IAsyncResult BeginWrite(byte[] buffer, int offset, int count, System.AsyncCallback callback, object? state) { throw null; }
+        public override System.IAsyncResult BeginRead(byte[] buffer, int offset, int count, System.AsyncCallback? callback, object? state) { throw null; }
+        public override System.IAsyncResult BeginWrite(byte[] buffer, int offset, int count, System.AsyncCallback? callback, object? state) { throw null; }
         public override void CopyTo(System.IO.Stream destination, int bufferSize) { }
         public override System.Threading.Tasks.Task CopyToAsync(System.IO.Stream destination, int bufferSize, System.Threading.CancellationToken cancellationToken) { throw null; }
         protected override void Dispose(bool disposing) { }