[release/8.0] Add missing delegating/override method in TlsStream

Add missing delegating/override method in TlsStream

Testing: I have validated that after those changes my local reproduction was no longer hitting this failure.

Author: rokonec

src/libraries/Common/src/System/Net/TlsStream.cs

@@ -68,6 +68,11 @@ public override Task WriteAsync(byte[] buffer, int offset, int count, Cancellati
             return _sslStream.WriteAsync(buffer, offset, count, cancellationToken);
         }
 
+        public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default(CancellationToken))
+        {
+            return _sslStream.WriteAsync(buffer, cancellationToken);
+        }
+
         public override int Read(byte[] buffer, int offset, int size)
         {
             return _sslStream.Read(buffer, offset, size);