[QUIC] Fix typo preventing freeing of TLS secrets (#120165)

Author: kitlith

src/libraries/System.Net.Quic/src/System/Net/Quic/Internal/MsQuicTlsSecret.cs

@@ -131,7 +131,7 @@ public unsafe void Dispose()
 
             QUIC_TLS_SECRETS* tlsSecrets = _tlsSecrets;
             _tlsSecrets = null;
-            NativeMemory.Free(_tlsSecrets);
+            NativeMemory.Free(tlsSecrets);
         }
     }
 }